A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool
Emily Oster
What the research actually shows — so you can make parenting decisions from evidence, not fear.
Oster, an economist at Brown, takes the most anxiety-producing parenting decisions — breastfeeding, sleep training, screen time, daycare — and examines what the research actually says. On many issues parents agonize over most, the difference between choices is far smaller than the guilt suggests.
Everything Oster wants you to walk away with
Studies show breastfeeding is associated with better outcomes, but those outcomes are also linked to education, income, and marital status. When researchers compared siblings — one breastfed, one not — the IQ effect disappeared entirely.
The confirmed benefits of breastfeeding are real but modest: fewer gastrointestinal infections and lower eczema in the first year, possibly fewer ear infections. There is no compelling evidence for 'smarty boobs.' The strongest benefit may actually be for mom — a 20-30% reduction in breast cancer risk.
Your circumstances differ. Your preferences differ. Your constraints differ. Breastfeeding may be empowering for one mother and miserable for another. Both are valid. This book won't tell you what to decide — it gives you the inputs so you can decide confidently.
If you want to collect data and make pretty graphs, go for it. But remember that this is the illusion of control, not actual control. Good-enough parenting across the major decisions matters far more than optimizing each individual choice.
People love a scary narrative. 'Formula-fed children more likely to drop out' gets clicks. 'Well-designed study shows small impacts on diarrheal diseases' does not. This desire for shock interacts poorly with most people's lack of statistical knowledge.
Multiple well-designed studies show sleep training improves infant sleep without negative effects on attachment, behavior, or cortisol levels. The benefits extend to parental mental health — sleep deprivation is a major contributor to postpartum depression.
Going a bit more in the exposure direction may be sensible. Your kid probably shouldn't lick the airport floor, but wiping down everything with hand sanitizer or bringing disposable placemats to restaurants is likely unnecessary after the first few months.
You'll still look pregnant for days or weeks. Sex can be painful. Breastfeeding promotes vaginal dryness. The hormone surge creates extreme emotional sensitivity. This is not the time to watch the first fifteen minutes of Up. Exercise, massage, and especially sleep are the first-line treatments.
Despite widespread warnings, there is simply no evidence that pacifier use impacts breastfeeding success. For premature infants especially, delayed cord clamping has strong evidence. Recommendations increasingly favor delaying the cord cutting when possible.
The book fights not against any particular piece of advice but against the idea of not explaining why. Armed with the evidence and a way to think about decisions, you can make choices right for your family. If you're happy with your choices, that's the path to happier parenting.
These notes are inspired by direct excerpts and woven together into a readable guide you can follow from start to finish.
By Emily Oster
One of the great themes of your parenting life is that you have way less control than you think you do. This book exists to help you navigate that reality with data rather than panic.
The challenge with parenting research is separating correlation from causation. Studies of breastfeeding, for example, consistently show that breastfed children have better school performance and lower obesity rates—but these outcomes are also linked with a mother’s education, income, and marital status. How do you know whether it is the breastfeeding or those other differences that drive the results? One answer is that some data is better than other data. Throughout this book, the approach is to use economic training—the part focused on teasing causality out of data—to separate the good studies from the less good ones.
The same data does not always lead everyone to the same decision. Data is an input, but so are preferences. In deciding whether to breastfeed, it is useful to know what the benefits are, but it is also crucial to think about the costs. You may hate breastfeeding; you may plan to return to work and hate pumping. These are reasons not to breastfeed. Too often we focus on the benefits at the expense of thinking about the costs.
Your choices can be right for you but also not necessarily the best choices for other people. Your circumstances differ, your preferences differ. In the language of economics, your constraints differ. This book will not tell you what decisions to make for your kids. Instead, it tries to give you the necessary inputs and a decision framework. The data is the same for us all, but the decisions are yours alone.
The goal is not to fight against any particular piece of advice but against the idea of not explaining why. Armed with the evidence and a way to think about decisions, you can make choices that are right for your family. If you are happy with your choices, that is the path to happier, more relaxed parenting—and, hopefully, to a bit more sleep.
A bath in the hospital is not a terrible thing, but there is also really no reason to bathe your newborn other than the gross-out factor. Most of the blood can simply be wiped off. Many families wait a week or two before giving a real bath at home.
Circumcision can be done more or less as soon as you confirm the penis is working properly—that is, after the first time the baby pees. The American Academy of Pediatrics suggests the health benefits of circumcision outweigh the costs, but notes correctly that both benefits and costs are quite small. This decision often comes down to personal preference, cultural considerations, or simply a desire to have your son’s penis look a particular way. These are all valid reasons to do it or not do it.
If you have the option to send your baby to the nursery for a few hours and you want to do that, you should not feel shame in doing so. There is no good evidence that you are disrupting your breastfeeding relationship. And if you find yourself falling asleep with the baby in the bed, ask for help.
Newborn weight loss is common and closely watched. The website newbornweight.org lets you enter time of birth, method of birth, method of feeding, birth weight, and current weight to learn where your child falls in the distribution. The major concern about weight loss is that it signals dehydration—but you can monitor that directly. If your baby is peeing with some frequency and does not have a dry tongue, there is a very good chance they are not dehydrated. Conversely, if you see those signs, supplementation may be a good idea even if weight loss is not severe.
Similarly, for jaundice there is a website, bilitool.org, that will tell you if treatment is recommended given your baby’s bilirubin levels.
For premature infants, there is very good evidence that you should delay cord clamping. On balance, the recommendations increasingly favor delaying the cord cutting for all newborns, if possible.
There are a variety of blankets that will allow you to successfully swaddle your baby so they cannot escape. The key is that these have some way of keeping your baby tucked in other than folding—for example, many yards of fabric or some Velcro. One popular option is the Miracle Blanket. Importantly, these risks of hip dysplasia arise if the baby’s legs are not able to flex at the hip, so it is crucial to swaddle in a way that allows them to move their legs around.
The most important thing is to try to take care of yourself. Infant crying is linked to postpartum depression and anxiety, and both parents will need a break. The cause of colic is poorly understood, so solutions are hard to develop. Many of the theories involve digestion—poorly developed gut flora or an intolerance to milk protein—and most proposed solutions relate to those theories.
Two treatments have some known success. The first is supplementation with a probiotic, which a number of studies have shown to reduce crying. The second is managing the baby’s diet, either by changing formula types or, if the baby is breastfed, changing the mother’s diet. One recommendation is to switch to a soy-based or hydrolyzed protein formula (most major formula makers have versions of these). The evidence on formula switching is mostly financed by formula companies, so do with that what you will, but it may be worth a try. If breastfeeding, the standard recommendation is the elimination of all dairy, wheat, eggs, and nuts—a pretty dramatic dietary change. Unfortunately, we do not know whether just one of these foods, all, or a combination makes the difference, and the evidence overall is pretty limited.
If you want to collect data and make pretty graphs about your baby, go for it—but remember that this is the illusion of control, not actual control.
As your child ages into toddlerhood and beyond, it is not necessarily a good idea to wipe down everything with hand sanitizer or bring disposable placemats to restaurants. Going a bit more in the exposure direction may be sensible. Your kid probably should not lick the floor at the airport, but moderate germ exposure seems fine.
Virtually all doctors suggest you try to avoid exposure to illness in the baby’s first couple of months. The smaller the child, the more vulnerable they are to serious complications. For very young infants, especially those younger than twenty-eight days, medical protocols call for much more aggressive interventions in response to illness.
There is some evidence that warm compresses on the perineum during the pushing stage of labor can prevent very severe tears. It will also likely hurt to poop after delivery; this depends on how traumatic your birth experience was. Stool softeners are commonly given to improve the first postbirth bowel movement.
A few days later, you are home. The most immediate consequences—heavy bleeding, uncomfortable first pee—will be over, but you will not feel normal. You will still look pregnant for a few days or weeks. Then you will have a bunch of floppy skin, which does resolve eventually (weeks or months later, not days). Even once the floppy skin is gone, many women find they have what is referred to as “mummy tummy,” a pouchy stomach that never quite snaps back.
Once you can exercise, it can be challenging to find time, but if it is important to you, you should try. Exercise can help combat postpartum depression and generally improves mood. Taking care of yourself also matters.
In the first days and weeks after your baby arrives, you will experience a wave of hormones. Most women are emotionally sensitive during this period—this is not, for example, the time to watch the first fifteen minutes of the movie Up. This early experience is sometimes called the “baby blues” and is self-limiting; the hormone surge is worst in the first few days after giving birth and dies down a couple of weeks later.
Treatment for postpartum depression proceeds in stages. For mild depression, the first line of treatment is to try to manage without drugs. There is some evidence that exercise or massage can be helpful. Perhaps most important is sleep—for new parents, lack of sleep can be a huge contributor to mild depression.
We know breast milk contains antibodies, so it is plausible that it protects against some illnesses. The most compelling study found two significant impacts: in the first year, breastfed babies had fewer gastrointestinal infections (i.e., diarrhea) and lower rates of eczema and other rashes. It seems reasonable to conclude that breastfeeding lowers infant eczema and gastrointestinal infections. For other illness outcomes, the most compelling evidence is in favor of a small reduction in ear infections.
Context matters for weighing these benefits. SIDS is rare—about 1 in every 1,800 births, and perhaps 1 in 10,000 among babies with no other risk factors. Ear infections and colds, in contrast, are common; your kids will get colds whether you breastfeed or not.
It is true that obesity and breastfeeding are correlated—kids who are breastfed are less likely to be obese later in life. But this correlation does not show causation; it does not prove that those kids who become obese do so because they were not breastfed.
One important study approached the IQ question in three phases. First, comparing breastfed and non-breastfed children with simple controls, researchers found large differences in child IQ. Second, after adjusting for the mother’s IQ, the effect was much smaller but still persisted. Third, they compared siblings born to the same mother—one breastfed, one not—which accounts for all differences between mothers. In this sibling analysis, breastfeeding did not have a significant impact on IQ, suggesting it is something about the parents, not anything about breast milk, driving the effect.
There is no compelling evidence for “smarty boobs.” The apparent link between breastfeeding and higher IQ appears driven by parental characteristics, not by breast milk itself.
One reason is that people seem to love a scary or shocking narrative. “Formula-Fed Children More Likely to Drop Out of High School” is a more clickable headline than “Large, Well-Designed Study Shows Small Impacts of Breastfeeding on Diarrheal Diseases.” This desire for shock interacts poorly with most people’s lack of statistical knowledge. There is no pressure on the media to focus on reporting the “best” studies, since people have a hard time separating the good studies from the less good ones.
For some women, breastfeeding makes them feel empowered and happy—it is convenient to have a ready food source, and they find nursing to be peaceful and relaxing. For others, breastfeeding makes them feel like a cow. They hate lugging the breast pump around. It is hard to tell if the baby is even getting enough food. Their nipples hurt. Many of the purported benefits of breastfeeding for moms are really subjective. One of the things on every pro-breastfeeding list is “saves money”—but that really depends. Formula is expensive, but so are nursing tops, nipple creams, nursing pads, and the many breastfeeding pillows you need to make it work. And, more importantly, there is your time, which is valuable.
There is one benefit with a larger and more robust evidence base: the link between breastfeeding and cancers, in particular breast cancer. Across a wide variety of studies and locations, there seems to be a sizable relationship—perhaps a 20 to 30 percent reduction in the risk of breast cancer. Since almost 1 in 8 women will have a form of breast cancer at some point, this reduction is big in absolute terms. The data is not perfect—controls for maternal socioeconomic status are almost always missing—but the case for causality is bolstered by concrete mechanisms: breastfeeding changes some aspects of the cells of the breast, making them less susceptible to carcinogens, and it lowers estrogen production, which can in turn lower breast cancer risk.
After all the focus on the benefits of breastfeeding for kids, it may be that the most important long-term impact is actually on Mom’s health.
The most convincing evidence on the value of breastfeeding may actually come from the experience of women who have done it and describe the satisfaction of closeness with their child. This is a great reason to do it and a good reason to try. It is also a good reason to support women who want to try and to not shame women who breastfeed in public. But it is not a good reason to judge yourself if you decide breastfeeding is not for you.
Moms who had their infants skin-to-skin after birth were more likely to still be breastfeeding at six weeks (72 percent versus 57 percent) and also reported less pain while being stitched up after birth. Despite the warnings you may hear, there is simply no evidence that the use of pacifiers impacts breastfeeding success. Smoking during pregnancy slows down milk production, as does obesity.
Good news: mostly, breastfeeding moms have no dietary restrictions. The only food women are medically advised to avoid during breastfeeding is high-mercury fish—no swordfish, king mackerel, or tuna. But other fish are fine, as are unpasteurized cheeses, sushi, rare steak, deli meats, and on and on. If your baby is suffering from colic, there is some evidence that avoiding common dietary allergens could help.
There is something of an old wives’ tale that gassy foods (cauliflower, broccoli, beans) lead to a gassy baby. Only one paper exists on this, based on a mail survey with significant problems in data collection and analysis—poor response rate, excessive response among people hyperconcerned about breastfeeding, and problems with statistical precision. It is safe to ignore it. Eat what you want.
Many women hear they should avoid alcohol altogether while breastfeeding, or that they should “pump and dump.” On the other side, some say beer will increase milk supply. Neither is really true. When you drink, the alcohol level in your milk is about the same as your blood alcohol level. The baby consumes the milk, not the alcohol directly, so the level of exposure is extremely low. One paper calculated that even if you had four drinks very quickly and then breastfed at peak blood alcohol level, the baby would be exposed to only a very, very low concentration—extremely unlikely to have any negative effects. On the flip side, drinking does not improve your milk supply; if anything, it may lessen it a bit.
Regarding medications while nursing, most are generally safe. You can search virtually any drug in the LactMed database online. The first line of defense for postbirth pain is Tylenol or ibuprofen, which are well tolerated and fine while breastfeeding. However, ibuprofen is not always enough, especially after a C-section. Codeine used to be a common next step, but more recent data shows it has significant nervous system effects in babies—making them extremely sleepy, with a few cases of severe consequences. Newer recommendations generally advise against codeine or other opioids like oxycodone for breastfeeding mothers.
If you have been on antidepressants before and know which one works for you, use that one. If not, the first-line SSRIs for nursing mothers are paroxetine and sertraline, which transfer to breast milk at the lowest levels.
As for caffeine, most people find it is fine while nursing, and there is no literature suggesting risks to the baby. However, some babies are quite sensitive and get fussy and irritable. If that is the case, you may have to avoid it. And hydration is important for everyone—take the water anywhere you can get it.
There are basically three reasons to use a breast pump. First, if you are struggling with low supply early on, your doctor may suggest pumping after feedings to increase supply—the theory is sound, though there is not much empirical evidence. If this is your only use, renting a higher-quality pump from the hospital may be a good idea. Second, many women pump early on to start giving the occasional bottle or to build a supply before returning to work. Many women report that it works well to choose one feeding—likely in the morning, when milk is most plentiful—and pump after that feeding. Over a week or two you will get enough to give a bottle. Third, the main use is to replace breastfeeding sessions after returning to work: you pump at approximately the same times the baby would eat, and they eat what you pumped the next day.
The latest recommendations from the American Academy of Pediatrics call for an empty, toy-free crib. Infants should sleep alone in a crib or bassinet, on their back, with nothing else in the crib—no bumpers, no blankets. The crib should be in the parents’ room. These recommendations are part of a safe sleep campaign designed to lower the risk of SIDS.
SIDS (Sudden Infant Death Syndrome) is the unexplained death of a seemingly healthy infant under one year old. Excluding birth defects, SIDS is the most common cause of death for full-term infants in the first year of life in the US. Ninety percent of SIDS deaths occur in the first four months. It seems to occur when a baby spontaneously stops breathing and doesn’t start again. It is more common in premature babies and in boys.
The medical recommendations to avoid SIDS have four components: infants should be (1) on their back, (2) alone in the crib, (3) in their parents’ room, and (4) with nothing soft around. Research shows that babies who sleep on their stomachs are roughly eight times more likely to die of SIDS. There is also a biological mechanism for this: babies tend to sleep more deeply on their stomachs, and SIDS risk is increased with deeper sleep. Overheating is also a risk factor—babies who died were more likely to be wearing heavy clothing, sleeping under a lot of bedding, or sleeping in a hot room.
One note: if your infant rolls over on their own, there is no need to go rolling them back. Once they can do this, the highest risk of SIDS has also passed, probably because the baby now has enough head strength to move their head to breathe more easily.
There is one substantial side effect of back sleeping: deformational plagiocephaly, or flat head. Infants who sleep on their back are at higher risk, and the frequency of this has been rising since the implementation of “Back to Sleep.”
Even in the lowest-risk group—neither parent smokes or drinks heavily, baby is breastfed—the data shows some elevated risk. The risk of SIDS death for infants who do not bed-share in this group is 0.08 per 1,000 births; for those who bed-share, it is 0.22 per 1,000 births. In context, the overall US infant mortality rate is around 5 deaths per 1,000 births, so this represents a very small increase relative to overall mortality. Another way to say it: among families with no other risk factors, roughly 7,100 of them would have to avoid co-sleeping to prevent one death.
Notably, there does not seem to be any elevated risk from co-sleeping after three months if both parents are not drinking or smoking. The main takeaway: if you are going to co-sleep, you should definitely not drink a lot or smoke, and neither should your partner. Limiting these behaviors will let you co-sleep in the safest way possible, although it will not completely eliminate the risks.
While one can debate the merits of room sharing at all, the AAP’s recommendation that it extend through the baby’s first year is problematic. Up to 90 percent of SIDS deaths occur in the first four months, so sleeping choices after four months are very unlikely to matter for SIDS. A 2017 study found that at four months, sleep was more consolidated (in longer stretches) for babies sleeping in their own room. At nine months, infants who slept alone slept longer—this effect was largest for those who moved to their own room by four months. Most notably, these differences were still present at age two and a half: children who slept alone by nine months slept forty-five minutes more per night than those still room-sharing at nine months. Sleep is crucial for child brain development; it is not just a selfish parental indulgence.
If you plan to sleep-train your child, success is very unlikely while the child is sleeping in your room. And most people sleep better without a child in the room—parents being well rested is important, too.
Across virtually all studies, the one thing that jumps out as really, really risky is babies sharing a sofa with an adult. Death rates from this are twenty to sixty times higher than baseline risk. An exhausted adult falls asleep holding an infant on a cushiony sofa, and it is easy for the infant to be smothered. Unfortunately, in at least some of these sofa deaths, the parent involved was trying to avoid bed-sharing risks—hoping that if they sit up, they will stay awake—and then fell asleep by accident. Even with the small risks of bed-sharing, you would be much better off sharing a bed than accidentally co-sleeping on a sofa.
Infants who die of SIDS are more likely to be found with blankets over their heads. The solution is the wearable blanket—a zipped-up bag you put your child in. Since there is no real reason to have another kind of blanket, this recommendation seems reasonable to follow.
Many aspects of scheduling will be kid-specific, and attempts to organize your baby are likely to meet with some variation. But not everything varies. One thing that does not show as much variation is wake-up times. Even at around five or six months, the majority of children wake between six and eight a.m. By age two, the range is smaller—six-thirty to seven-thirty a.m.
The unscheduled mess of the first year does end. Your baby will, eventually, arrive at a more predictable sleep schedule—maybe not right away, maybe not exactly the one you envisioned, but they will get there. This is perhaps the most reassuring thing of all.
In the 1950s, about five hundred people, mostly children, died of measles each year in the US, and 3 to 4 million were sickened. In 2016, zero children died of measles, and there were an estimated eighty-six cases. The reason is simple: the development of a measles vaccine. Vaccinations are among the most significant public health triumphs of the past hundred years. Millions of lives worldwide have been saved by vaccines for diseases like whooping cough, measles, smallpox, and polio. The chicken pox vaccine has prevented a tremendous amount of discomfort and some deaths. The hepatitis B vaccine has reduced liver cancer. The HPV vaccine has the potential to significantly lower rates of cervical cancer.
Areas with more educated parents actually have, on average, lower vaccination rates—suggesting it is not lack of information getting in the way. The scientific consensus is extremely clear: vaccines are safe and effective, supported by a wide range of doctors, medical organizations, and government and non-government entities.
It is not fair to say there are no risks at all. For many vaccines (all but the DTaP), there is a risk of allergic reaction—but this is extremely rare (about 0.22 in 100,000 vaccines) and treatable with Benadryl or, in extreme cases, an EpiPen. Fainting sometimes occurs after vaccination, mostly among adolescents; this does not have long-term consequences.
There are three documented cases in the history of vaccination where the measles vaccine caused disease in immune-compromised children. This is categorized as a convincing link, but it does not mean this is a risk everyone should worry about—it arises only in immune-compromised children, and even then is vanishingly rare. Similar issues arise for immune-compromised children who get the chicken pox vaccine.
The MMR vaccine is linked with febrile seizures—seizures occurring in infants or young children in association with high fever. About 2 to 3 percent of US children will have a febrile seizure before age five (most are not vaccine-associated). These seizures are about twice as likely in the ten days after the MMR vaccine. They are actually more likely for children who get their first dose later (older than one year), which is a reason to vaccinate on time rather than delay.
The largest study on this includes 537,000 children—all children born in Denmark from 1991 to 1998. Researchers linked vaccination information to later diagnosis of autism or autism spectrum disorders and found no evidence that vaccinated children are more likely to be autistic; if anything, results suggest vaccinated children are less likely to be diagnosed with autism. Many similar studies exist. One focuses specifically on children with an older sibling with autism—a higher-risk group—and again found no link with the MMR vaccine. There is no mechanism by which this would occur, and controlled studies in monkeys show no plausible relationship.
Your child may well get a fever from a vaccine. It is possible, though quite unlikely, that this fever could lead to a seizure. It is also possible, though very, very unlikely, that they could have an allergic reaction. But it is reasonable to say there is no evidence of significant long-term consequences of vaccines for healthy children.
Natural experiments in countries that changed parental-leave policies let us compare outcomes of children born under different policies without worrying about underlying differences across parents. By comparing children born during a six-month maternity leave policy to those born under a year-long policy, we can study the effects of leave on child outcomes. The bottom line: these parental leave extensions have no effect on child outcomes—no effects on test scores, on income later in life, or on anything else. In many cases, the studies have very long follow-up periods; we can say that one year of parental leave versus two years does not influence a child’s high school test scores or earnings in early adulthood.
For the impact of parents working when children are older, we are limited to correlational studies. When we look at schooling, test scores, and school completion, these correlations tend to be about zero. Two parents working full-time has a similar effect to one parent working and one not.
The weight of the evidence suggests the net effects of working on child development are small or zero. Depending on your household configuration, these effects could be a little positive or a little negative. But this is not the decision that will make or break your child’s future success.
Childcare is expensive, and most of it is paid in after-tax income. Your income needs to be considerably more than the cost of childcare to break even. Consider a family with total income of $100,000, each parent making $50,000. After taxes, take-home pay is about $85,000. If both parents work and pay $1,500 a month for childcare, their disposable income after childcare is about $67,000. If one parent stays home, the family makes less (about $46,000 take-home) but pays nothing for childcare. The difference in take-home income is about half what it would be without children. This calculus gets more complicated if childcare is more expensive—a full-time nanny, especially with legally required taxes in an expensive area, can run $40,000 to $50,000 a year, completely wiping out one parent’s income.
In economics, the advice is to “solve the tree” by working backward. First, decide what nanny you would want if you had to have a nanny. Then decide what day care you would want if you had to have day care. Then compare those two optimal options. Rather than comparing the wide range of options in each category, you face a very specific choice: your “optimal” day care setup versus your “optimal” nanny setup.
Research found that attending higher-quality day care strongly correlated with better child language development—kids who went to better day cares seemed to talk more. When researchers looked at behavior problems, there did not seem to be a relationship to day care quality in either direction. These results held through sixth grade: day care quality was associated with better vocabulary outcomes but not with behavior. Of course, higher-quality day care is more expensive, so a different set of kids are enrolled. The study adjusted extensively for family background, including home visits to evaluate parenting quality. Parenting matters a lot—way more than day care—but the day care results remained even after adjusting for observed parenting differences.
When evaluating caregivers, look at the basics: Is the adult available and interacting with the children, or are they on their phone? Do they have positive physical contact with the children—reinforcing good behavior with a hug, holding the baby? Then consider developmental stimulation: Does the adult read to the children? Talk to them? Respond when the baby makes a noise? Finally, there is behavior: how does the adult respond when children act out? Do they physically restrain the children, hit, or speak negatively? These would all be very bad signs.
More months in day care before eighteen months are associated with slightly lower cognitive scores by four and a half, but more time in care after eighteen months is associated with higher cognitive outcomes. It could be that early on, one-on-one attention enhances language development, while at older ages, day care offers more exposure to letters, numbers, and social integration. Studies that combine the periods suggest that overall the effect is positive—kids in day care for more total time have better language and cognitive outcomes at four and a half.
Are kids in day care less attached to their moms? No. Quality of parenting matters for attachment, but day care time makes no difference. Kids in day care are more likely to get sick—mostly colds, fevers, and stomach flu—but these early exposures seem to confer some immunity, with fewer colds in early elementary school for those who were in day care longer as toddlers.
Two things come up again and again: First, parenting matters more than childcare type. Having books in your house and reading them to your kid will matter much more than what books they have at day care. Second, childcare quality matters much more than which type of childcare you have. A high-quality day care is likely better than a low-quality nanny, and vice versa.
On average, a nanny is more expensive than day care, though a nanny-share arrangement may offset some of the cost. Beyond budget, consider convenience: Is there a day care close to home or work, or will you have to drive far out of your way? What are your options if your child gets sick? At-home care can still work with a sick kid, but day care cannot.
Yes. There are many, many studies employing a variety of related procedures, many of them randomized trials. A 2006 review covered nineteen studies of “Extinction” (leave and do not return), of which seventeen showed improvements in sleep. Another fourteen studies used “Graduated Extinction” (come in at increasingly lengthy intervals), and all showed improvements. A smaller number covered “Extinction with Parental Presence” (stay in the room but let the child cry), which also showed positive effects. These effects persist through six months or a year in studies with longer follow-up—children who are sleep-trained sleep better on average even a year later. These methods do not completely solve all sleep problems from day one, and some children respond better than others, as do some parents.
| Method | How It Works | Evidence Snapshot |
|---|---|---|
| Extinction | Put baby down and do not return unless safety/needs require it. | Most studied; strong evidence that it improves sleep. |
| Graduated Extinction | Return at increasing intervals for brief check-ins. | Strong evidence; often easier for parents to sustain. |
| Parental Presence | Stay in room while limiting interaction. | Positive results in smaller evidence base. |
Evidence supports all three. Some reports find Graduated Extinction is easier for parents; others find it prolongs crying. The only general principle: consistency is key. Choosing a method and sticking with it increases success.
Most studies and virtually all sleep books recommend a bedtime routine as part of any sleep intervention. There is not much direct evidence—one review calls it a “common sense recommendation”—but it is generally included with all approaches. The idea is to have activities that signal bedtime: putting on pajamas, reading a book, singing a song, turning off the lights.
Sleep training methods consistently improve parental mental health, including less depression, higher marital satisfaction, and lower parenting stress. In some cases the effects are very large: one small study reported that 70 percent of mothers met criteria for clinical depression at enrollment and only 10 percent after the intervention. The fact that sleep training is good for parents should not be ignored. And sleep is also beneficial to development for babies and kids—settling into a good routine could have long-term positive effects.
A 2006 review of sleep training studies, including thirteen different interventions, noted that adverse secondary effects were not identified in any of the studies. On the contrary, infants who participated in sleep interventions were found to be more secure, more predictable, less irritable, and to cry and fuss less following treatment. More recent studies draw the same conclusion—the babies are better rested, the parents are better rested, and everyone is in a better mood.
“Cry it out” works, helps parents and kids sleep better, and improves parental mood and happiness.
Some experts suggest sleep training as early as eight or ten weeks. At this age, most babies cannot sleep through the night without eating—you should not expect your two-month-old to sleep for twelve hours. The goal at that age is to encourage the baby to fall asleep on their own at the start of the night and then only wake when hungry. A ten- or eleven-month-old, on the other hand, should be able to go through the night without eating, and training at that age focuses on both falling asleep independently and staying asleep through the night. The goal of sleep training is not to deprive your child of basic needs like food and diaper changes—it is to encourage going to sleep independently once those needs are met.
In a landmark randomized study, children who were exposed to peanuts were far less likely to be allergic at age five. In the group that did not get peanuts, 17 percent were allergic at five. In the group that received peanuts, only 3 percent were allergic. Since the study was randomized, there was no reason other than peanut exposure for the difference, and it showed up in both high- and low-allergy-risk groups. Early exposure to peanuts is now the normal recommendation, especially for children at risk for an allergy.
Research shows that babies whose mothers ate more of a particular food during pregnancy or breastfeeding were more likely to prefer that food. This suggests that flavor exposure through the placenta and breast milk affects whether children are receptive to new flavors. Once children start eating solid foods, randomized evidence shows that repeated exposure to a food—say, giving kids pears every day for a week—increases their liking of it. This works for fruits and also for vegetables, even bitter ones.
Most kids become more picky around two and then slowly grow out of it during their elementary school years. This can surprise parents whose eighteen-month-old ate everything. Kids are more likely to try foods with “autonomy-supportive prompts” like “Try your hot dog” or “Prunes are like big raisins, so you might like them.” They are less likely to try things if parents use “coercive controlling prompts” like “If you finish your pasta, you can have ice cream” or “If you won’t eat, I’m taking away your iPad.”
The vast majority of allergies result from eight food types: milk, peanuts, eggs, soy, wheat, tree nuts, fish, and shellfish. Importantly, the research is about regular exposure, not just a one-time introduction—you need to actually keep giving your child the food regularly. Go slowly: try a little bit at first, only one allergenic food in a given day, and see how they react. If nothing happens, give a little more, until you work up to a normal amount.
Soda is strongly discouraged for infants and children (and adults). Juice is more controversial, but generally, young children should have formula, breast milk, or, once they start eating solid foods, water. Choking hazards—nuts, whole grapes, hard candies—are to be avoided for obvious reasons. Grapes are okay in pieces, nuts are okay in nut-butter form, and hard candies are not recommended for other reasons.
Cow’s milk is more complicated because it interacts with allergen issues. It is important to introduce some milk-based foods—yogurt, cheese—to avoid allergies, but milk itself as a primary drink is not recommended for infants. The concern is that cow’s milk is not a complete infant nutrition system, and if your infant drinks a lot of it, it will restrict formula or breast milk intake. Infants who have cow’s milk as their primary milk source are more likely to be iron-deficient. As an addition to oatmeal or cereal, it is not a problem.
The concern with honey is infant botulism—a serious disease in which a toxin interferes with neurological functions, including the infant’s ability to breathe. It is most common under six months, treatable with a very high success rate, though the treatment requires the baby to be hooked up to a breathing machine for a few days. The toxin Clostridium botulinum is found in soil and in honey, and multiple case reports from the 1970s and ’80s of infant botulism associated with honey led to the recommendation against honey through the first year of life.
If you eat a typical varied diet, even one that is pretty unhealthy, you are very unlikely to be seriously deficient in any vitamins. Your toddler or young child does not generally need a multivitamin. Even a child who seems like a very picky eater will be getting enough vitamins. A breastfed baby will get most vitamins through breast milk.
The two possible exceptions are vitamin D and iron. Vitamin D is not present in many foods and not in high concentrations in breast milk. People get vitamin D through sun exposure, but many of us live in houses in cold places. As a result, a lot of infants and children are considered deficient—as much as a quarter or more of white children, and higher among children of color (darker skin lowers vitamin D absorption from the sun). What is less clear is whether this deficiency has much actual health impact. In two small randomized trials of supplementation, there were no impacts on bone growth or bone health, even though supplementation did increase vitamin D concentrations. This does not mean you should not supplement—rickets does occur, primarily in developing countries with serious nutritional limits—but if you miss a day here or there, you should not panic.
Pediatricians focus on three key checkpoints. At 9 months: rolling both sides, sitting with support, motor symmetry, grasping and transferring objects between hands. At 18 months: sitting, standing, and walking independently; grasping and manipulating small objects. At 30 months: doctors look for subtle gross motor errors and loss of previous skills (a marker of progressive disease). The 9- and 18-month milestones are the most crucial; by 30 months, most major issues have been well identified.
There is enormous variation in when children hit physical milestones. Sitting without support ranges from 3.8 to 9.2 months. Standing with assistance ranges from 4.8 to 11.4 months. Crawling (which 5 percent of kids never do) ranges from 5.2 to 13.5 months. Walking with help ranges from 5.9 to 13.7 months. Standing alone ranges from 6.9 to 16.9 months. Walking alone ranges from 8.2 to 17.6 months.
Kids younger than school age get an average of six to eight colds a year, most of them between September and April—about one a month. These colds last on average fourteen days. A month is thirty days. So in the winter, your kid will have a cold roughly 50 percent of the time. Most colds end with a cough that can last additional weeks. Most are minor, though they increase the risk of ear infection and other prolonged bacterial infections like bronchitis or walking pneumonia. Most doctors will tell you to come in if you are concerned, if a fever lasts longer than a couple of days, or if your child gets worse after seeming to get better. Ear infections are the most common complication—about a quarter of kids will have one by age one, and 60 percent by age four.
Colds do not respond to antibiotics (they are caused by a virus), and your doctor should not prescribe them. Globally, overuse of antibiotics is a public health problem because it contributes to antibiotic resistance. Even for your particular kid, antibiotics are not risk-free—they can contribute to diarrhea, for example. The move toward prescribing antibiotics sparingly is a good thing.
Research shows that children under two cannot learn much from screens. In studies testing whether babies could learn actions from video, twelve-month-olds learned nothing from the video demonstration, while older kids learned much less than from seeing a live person do it. In another study, researchers tried to maintain exposure of English-speaking nine- to twelve-month-olds to Mandarin language sounds through either a live person or a DVD. The live person worked well; the DVD did not.
What does matter for language development at this age is books. The most significant predictor of both how many words children spoke and how fast their vocabularies grew was whether their parents read to them. Similar results hold for children up to age two.
Slightly older children can learn from television. Kids learn songs from movies and shows, and can pick up names of characters and basic plot elements. Lab research has shown that three- to five-year-olds are able to learn words from television.
In the case of Sesame Street, there is actually good research suggesting that exposure increases school readiness in kids ages three to five. Early randomized trials found improvements in various measures of school readiness, including vocabulary, over a two-year period. A more recent study compared kids who got early access to the show (because of better TV reception) to those who got later access; the earlier-access kids were less likely to be held back in school at older ages. The show had bigger positive effects for children from more disadvantaged backgrounds.
One study reported that watching more TV under age three lowered test scores by a small amount—the equivalent of a couple of IQ points. However, watching TV at older ages did not seem to matter. Kids who watched little TV before age three and then a lot between ages three and five had test scores no different from—and if anything slightly higher than—those who watched little TV throughout.
If the alternative to an hour of TV is a frantic and unhappy parent yelling at their kid for an hour, there is good reason to think the TV might actually be better.
Parents often worry about whether their child is talking early or late relative to peers. The key takeaway from the research is reassuring: early talking does not guarantee later success, even at four, and late talkers mostly look like everyone else within a few years.
There are two broad approaches to potty training, and they trade off differently depending on age. An eighteen-month-old is much less likely to simply decide they will not poop in the potty no matter what you say—they have less will to defy you, which may make them easier. On the other hand, a three-year-old can be reasoned with and, yes, bribed. They have more will to defy you, but you can take advantage of their better ability to understand and control themselves.
On one side is a more goal-oriented approach, where you actively work toward toilet use on a defined timeline. On the other is a more laissez-faire approach, where you let the child lead with the timing that works for them, looking for signs of readiness and encouraging toilet use when they become apparent.
| Approach | Potential Upside | Potential Tradeoff |
|---|---|---|
| Goal-Oriented (Earlier Start) | Possible earlier completion when done consistently. | Can feel intense; resistance battles may be tougher. |
| Child-Led (Later Start) | Often calmer process with fewer power struggles. | May complete later and take longer overall. |
You will try anything—literally anything—to get your child to use the bathroom, but you cannot actually force them. Some kids respond to stickers, some to M&M’s, maybe some to meatballs. Potty training is really about what works for your family and your kid. The evidence suggests it is possible to train at a younger age than is now typical if you adopt a goal-oriented approach. Or you can wait until your child decides they are ready, which will probably be around three or a bit older. The child-led approach may take longer but may also be more pleasant for you.
Doctors generally do not worry about lack of nighttime dryness until a child is six years old.
Before getting into evidence, it is worth stepping back and thinking about why we want to discipline our kids. The answer is the same as what we are trying to do with all our other parenting choices: raise happy, nice, productive adults. When your kid refuses to clean up a mess and you discipline that behavior, it is not really that you want help cleaning up—it would be faster to do it yourself. It is that you are trying to teach them to take responsibility for their messes, both the LEGO messes now and the inevitable non-LEGO messes of the future. This is the discipline-as-education philosophy: discipline is not the same as punishment. There is a punishment component, but it is in the service of raising better humans, not punishment for its own sake.
There are a number of evidence-based parenting interventions, including 1-2-3 Magic, the Incredible Years, Triple P (Positive Parenting Program), and others. Many schools, including those with children who have serious behavioral issues, use a similar program called Positive Behavior Interventions and Supports.
For example, 1-2-3 Magic develops a system of counting (to three, obviously) in the face of disruptive behavior. If three is reached, there is a defined consequence—a time-out, loss of a privilege, and so on. There is a strong emphasis on consistency: whatever system you use, use it every time, including in the grocery store. If you say no to something, you stick to no. If your kid asks for dessert and you say no, you cannot later say yes if they whine long enough—what do they learn from that? That whining sometimes works. And similarly, do not make threats you cannot carry out.
One of the main tenets of these parenting approaches is that discipline should be reserved for actual bad behavior, not for things that are merely annoying. Toddler discipline is, really, parental discipline.
Research has found that spanking does have negative long-term impacts, especially on behavior problems. Spanking at age one increased behavior problems at three, and spanking at three increased behavior problems at five. These results held even with controls for earlier behavior—spanking at three relates to behavior problems at five even controlling for behavior problems at three. There is correspondingly no evidence that spanking improves behavior. If hitting is the alternative, one of the evidence-based programs described above is probably worth a try.
There is a large, well-established body of literature showing that children whose parents read to them as babies and preschoolers have better performance on reading tests later. Rather than just reading a book, kids benefit from being asked open-ended questions: “Where do you think the bird’s mother is?” “Do you think it hurts Pop when the kids hop on him?” “How do you think the Cat in the Hat is feeling now?”
Is it a good idea to put your child in preschool? The evidence from the day care chapter showed that more time in day care after eighteen months was associated with better language and literacy development at slightly later ages. This is about the best evidence we have that preschool might be a good idea. Many of the quality measures discussed in the day care section apply here, too—is the area safe, do the adults seem engaged, and so on.
The three philosophies you will most commonly encounter are Montessori, Reggio Emilia, and Waldorf. Montessori focuses on a particular classroom structure and set of materials, with emphasis on fine motor skills. Children’s play is referred to as “works,” and even young children are exposed to letters, numbers, writing in sand, counting blocks, and so on. Reggio Emilia–inspired schools put more emphasis on play, with typically little formal letter or number exposure at preschool ages. Waldorf schools have a heavy outdoor component, are largely play-based, focus on learning through play and art, and tend to include a domestic activity component—cooking, baking, gardening.
All three methods have a structured day so kids know what to expect. They all acknowledge that young kids benefit from exploring in a safe environment and self-directing, to some extent, in what they do.
We simply do not have a lot of concrete data to guide you on which preschool philosophy is best. Further complicating both research and decision-making, it is possible—even likely—that the best type of preschool will vary by individual child.
Research shows that parenthood hastens marital decline. Studies find that people who are happier before they have kids recover better, and that planned pregnancies are less impactful than unplanned ones. The effects are not enormously large—many people are still, on net, happy with their spouse. Just, slightly less.
Two specific factors play a role in this decline. The first is unequal chore allocation: women tend to do the bulk of household work even if they also work outside the home. The second is a decline in sex: parents have less sex, and sex makes people happy.
Sleep is a key issue. Drops in marital satisfaction are higher in couples with kids who sleep less. Lack of parental sleep contributes to depression in both parents and correspondingly to less happy marriages. You need sleep to function, and sleep deprivation affects your mood. If you are cranky, you are cranky with your partner.
Some small-scale randomized interventions show effectiveness. One is the “marriage checkup”—an annual meeting, possibly facilitated by a professional, to actually discuss your marriage. What do you feel is working? What is not? Are there particular areas of concern or unhappiness? These checkups seem to result in improvements in intimacy and marital satisfaction. Beyond this particular intervention, there is other evidence in favor of therapy more generally—group couples therapy, counseling programs beginning before birth and continuing after—to improve relationships. Broadly, these focus on communication and positive solutions to conflict.
When researchers analyzed the effects of birth spacing on the older child, they found that test scores were higher if there was more space between siblings. This may reflect more parental time invested in reading or other skill development at young ages. The effects, though, were pretty small.
The bulk of the evidence suggests there are some small risks, both short and possibly long term, to very short birth intervals. Waiting until the first child is at least a year old to get pregnant again may be a good idea. It also may just be easier on you as a parent, given the intensity of the infant stage.
Parenting cannot be about thinking about every possible eventuality, every possible misstep. Sometimes you just need to let it go. It makes sense to take parenting seriously and to want to make the best choices for your kid and for you. But there will be many times that you need to trust that if you are doing your best, that is all you can do. Being present and happy with your kids is more important than worrying about every small thing.
Use data where it is useful. Make the right decisions for your family. Do your best. And sometimes, just try not to think about it.