Introduction — The Data Behind the Decisions
One of the great themes of your parenting life is that you have way less control than you think you do. Studies of breastfeeding 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. Using an economist’s training to tease causality out of data, it becomes possible to separate the good studies from the less good ones.
But the same data does not always lead to the same decision. Data is an input, but so are preferences. You may hate breastfeeding. You may plan to return to work and hate pumping. Too often we focus on the benefits at the expense of thinking about the costs. Your choices can be right for you and also not the best choices for someone else.
This book will not tell you what decisions to make for your kids. It offers the necessary inputs and a decision framework. Armed with the evidence and a way to think about decisions, you can make choices that are right for your family.
Chapter 1 — The First Three Days
A hospital bath is not a terrible thing, but many families wait a week or two before giving a real bath at home. Circumcision can be done as soon as the baby pees; the AAP suggests health benefits outweigh costs, but notes correctly that both are quite small — the decision often comes down to personal preference or cultural considerations. If you want to send your baby to the nursery for a few hours, feel no shame — there is no good evidence you are disrupting your breastfeeding relationship.
Newborn weight loss is common and closely watched. The main concern is dehydration, which you can monitor directly: if your baby is peeing with some frequency and does not have a dry tongue, they are very likely not dehydrated. A website called newbornweight.org lets you enter feeding method, birth weight, and current weight to see where your child falls. For jaundice, bilitool.org will tell you whether treatment is recommended given your baby’s bilirubin level. On cord clamping, the evidence increasingly favors delaying the cut, especially for premature infants.
Chapter 2 — Wait, You Want Me to Take It Home?
Whatever swaddle blanket you choose, it is crucial to swaddle in a way that allows the baby to move their legs and flex at the hip — the risk of hip dysplasia arises specifically when those movements are restricted.
The most important thing when a baby cries constantly is to take care of yourself. Infant crying is linked to postpartum depression and anxiety in both parents, and both will need a break. The cause of colic is poorly understood. Two treatments have shown some success: supplementation with a probiotic, which several studies have shown to reduce crying, and managing the baby’s diet — either by changing formula types or, if breastfeeding, eliminating dairy, wheat, eggs, and nuts from the mother’s diet.
As your child ages into toddlerhood, wiping down everything with hand sanitizer is probably unnecessary — moderate germ exposure seems fine. Doctors are reasonably lax about germ exposure once a baby is a few months old. The reason they are not lax in the first couple of months is that for very young infants under twenty-eight days, medical protocols call for much more aggressive interventions.
Chapter 3 — Trust Me, Take the Mesh Underwear
There is some evidence that warm compresses on the perineum during pushing can prevent very severe tears. Stool softeners are commonly given to ease the first postbirth bowel movement. You will not feel normal for days or weeks. Many women also find they have what is referred to as “mummy tummy,” a pouchy stomach that never quite snaps back. Exercise can help combat postpartum depression and generally improves mood.
Sex after childbirth can be painful — breastfeeding promotes vaginal dryness and lowers sex drive, and injuries during birth can have persistent effects. And many women, after having a small person attached to them nearly constantly, really do not want to be touched. That is normal. The early wave of hormones is sometimes called the “baby blues” and is self-limiting, dying down a couple of weeks after birth. For postpartum depression that extends beyond baby blues, the first line for mild cases is to manage without drugs. Perhaps most important is sleep.
Chapter 4 — Breast Is Best? Breast Is Better? Breast Is About the Same?
The most compelling study found two significant impacts of breastfeeding: in the first year, breastfed babies had fewer gastrointestinal infections and lower rates of eczema and other rashes. For other illness outcomes, the most compelling evidence is in favor of a small reduction in ear infections. SIDS is rare — about one in every 1,800 births; ear infections and colds are common regardless.
It is true that obesity and breastfeeding are correlated — breastfed kids are less likely to be obese later. But this correlation does not show causation. On IQ, researchers first found large differences between breastfed and non-breastfed children. Then they added an adjustment for the mother’s IQ, and much of the breastfeeding effect disappeared. The crucial phase was comparing siblings born to the same mother, one breastfed and one not — this approach accounts for all differences between mothers. In this sibling analysis, breastfeeding had no significant impact on IQ. It is something about the parents, not anything about breast milk, that drives the association.
There is one benefit with a larger and more robust evidence base: the link between breastfeeding and breast cancer. Across a wide variety of studies, there seems to be a sizable relationship — perhaps a 20 to 30 percent reduction in the risk of breast cancer. Since almost one in eight women will have a form of breast cancer, this reduction is big in absolute terms. The case for causality is bolstered by concrete mechanisms: breastfeeding changes some aspects of breast cells, making them less susceptible to carcinogens, and it lowers estrogen production. After all that focus on benefits for the child, it may be that the most important long-term impact is actually on Mom’s health.
For some women, breastfeeding is empowering and convenient. For others, it makes them feel like a cow. They hate lugging the breast pump around. Their nipples hurt. The most convincing personal case for breastfeeding comes from women who describe the satisfaction of closeness with their child. This is a great reason to try — but not a good reason to judge yourself if you decide breastfeeding is not for you.
Chapter 5 — Breastfeeding: A How-To Guide
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. Despite the warnings you may hear, there is no evidence that pacifier use impacts breastfeeding success. The only food medically advised to avoid is high-mercury fish — no swordfish, king mackerel, or tuna. The gassy-foods-make-a-gassy-baby claim rests on a single poorly designed mail survey — it is safe to ignore it. Eat what you want.
On alcohol: when you drink, the level in your milk is about the same as your blood alcohol level. Even if you had four drinks quickly and breastfed at peak blood alcohol level, the baby would be exposed to only a very low concentration. Drinking does not improve milk supply; if anything, it may lessen it a bit. Most medications are safe while nursing — search virtually any drug in the LactMed database online. Codeine has significant nervous system effects in babies and is generally advised against for nursing mothers. The first-line SSRIs for nursing mothers are paroxetine and sertraline, which transfer to breast milk at the lowest levels.
There are basically three reasons to use a breast pump: to increase supply early on; to build a supply before returning to work; and to replace breastfeeding sessions after returning to work. A hands-free pumping bra is essential. Even a great pump is not as effective as your baby at milk removal — some women who breastfeed successfully never get any milk from a pump, and that variation is normal.
Chapter 6 — Sleep Position and Location
The AAP recommends that infants sleep alone on their back in a bare crib — no bumpers, no blankets — in the parents’ room. These recommendations are designed to lower the risk of SIDS, the unexplained death of a seemingly healthy infant under one year old. Ninety percent of SIDS deaths occur in the first four months. Babies who sleep on their stomachs are roughly eight times more likely to die of SIDS. Overheating is also a risk factor. If your infant rolls over on their own, there is no need to roll them back — once they can do this, the highest SIDS risk has passed.
Even in the lowest-risk group, co-sleeping carries some elevated risk. The risk of SIDS death for infants who do not bed-share is 0.08 per 1,000 births; for those who bed-share, it is 0.22 per 1,000 births. Roughly 7,100 families would have to avoid co-sleeping to prevent one death among those with no other risk factors. There does not seem to be any elevated risk from co-sleeping after three months if both parents are not drinking or smoking.
The AAP recommendation that room-sharing extend through the first year is problematic. A 2017 study found that at four months, sleep was more consolidated for babies in their own room. Children who slept alone by nine months slept forty-five minutes more per night than those still room-sharing at nine months, and this difference persisted at age two and a half. The one thing that stands out as really risky across all studies is babies sharing a sofa with an adult — death rates are twenty to sixty times higher than baseline. Even with the small risks of bed-sharing, you would be much better off sharing a bed than accidentally co-sleeping on a sofa.
Chapter 7 — Organize Your Baby
Many aspects of scheduling will be kid-specific, and attempts to organize your baby are likely to meet with variation. One thing that does not vary much is wake-up time: even at around five or six months, most children wake between six and eight in the morning. By age two, the range narrows to six-thirty to seven-thirty.
The other thing you realize with a second child is that the unscheduled mess of the first year does end. Your baby will eventually arrive at a more predictable sleep schedule. This is perhaps the most reassuring thing of all.
Chapter 8 — Vaccination: Yes, Please
In the 1950s, about five hundred people, mostly children, died of measles each year in the United States. In 2016, zero children died of measles, and there were an estimated eighty-six cases. Vaccinations are among the most significant public health triumphs of the past hundred years, and the scientific consensus is extremely clear: vaccines are safe and effective. Allergic reactions occur at about 0.22 per 100,000 vaccines and are treatable. The MMR vaccine is linked with febrile seizures at roughly twice the typical rate in the ten days after vaccination — not dangerous long-term, and notably more likely for children who get their first dose after age one, which is a reason to vaccinate on time.
On vaccines and autism, the largest study includes 537,000 children born in Denmark from 1991 to 1998 and found no evidence that vaccinated children are more likely to be autistic. One study focusing specifically on children with an older sibling with autism also found no link with MMR. There is no mechanism by which this would occur, and controlled studies in monkeys show no plausible relationship. It is reasonable to say there is no evidence of significant long-term consequences of vaccines for healthy children.
Chapter 9 — Stay-at-Home Mom? Stay-at-Work Mom?
Natural experiments in countries that changed parental-leave policies allow researchers to compare outcomes without the confounding of underlying parent differences. The bottom line: parental leave extensions have no effect on child outcomes — no effects on test scores, income later in life, or anything else across very long follow-up periods. For parents working when children are older, correlational studies also tend to find effects about zero. Two parents working full-time has a similar effect to one parent working and one not. This is not the decision that will make or break your child’s future success. The financial math matters too — a full-time nanny can run $40,000 to $50,000 a year in an expensive area, completely wiping out one parent’s income.
Chapter 10 — Who Should Take Care of the Baby?
In economics, the advice is to “solve the tree” by working backward: decide what nanny you would want if you had to have one, then what day care you would want, then compare the two optimal options directly.
Research found that higher-quality day care strongly correlated with better child language development through sixth grade, but no relationship to behavior problems. Parenting matters a lot — way more than day care — but the quality results remained after adjusting for parenting differences. More months in day care before eighteen months are associated with slightly lower cognitive scores by age four and a half, but more time after eighteen months is associated with higher cognitive outcomes. Kids in day care are more likely to get sick early on, but these exposures confer some immunity, with fewer colds in early elementary school.
Two things come up again and again: parenting matters more than childcare type, and childcare quality matters more than which type you have. Whatever childcare you choose, have a plan for who is in charge when the nanny or the kid is sick. The evidence suggests day care is worse early on and better at slightly older ages — which could argue for a nanny arrangement in the first year or eighteen months, followed by day care later.
Chapter 11 — Sleep Training
Good news: yes, sleep training works. A 2006 review covered nineteen studies of “Extinction” — cry-it-out in which you leave and do not return — of which seventeen showed improvements. Another fourteen studies used “Graduated Extinction,” where you come in at increasingly lengthy intervals, and all showed improvements. These effects persist through six months or a year. Sleep training also consistently improves parental mental health — less depression, higher marital satisfaction, lower parenting stress. In one study, 70 percent of mothers met criteria for clinical depression at enrollment and only 10 percent after the intervention. Adverse secondary effects were not identified in any of thirteen interventions studied — on the contrary, infants who participated were more secure, more predictable, less irritable, and cried less.
Ferber is a proponent of Graduated Extinction, while Weissbluth favors straight Extinction. The only general principle is that consistency is key. Weissbluth suggests you can begin as early as eight or ten weeks — at that age, the goal is to encourage the baby to fall asleep on their own at the start of the night and wake only when hungry. A ten- or eleven-month-old should be able to go through the night without eating. The goal of sleep training is not to deprive your child of basic needs; it is to encourage going to sleep independently once those needs are met.
Chapter 12 — Beyond the Boobs: Introducing Solid Food
In a landmark randomized study, children who were exposed to peanuts early were far less likely to be allergic at age five: 17 percent who did not get peanuts were allergic versus only 3 percent who did. Early exposure to peanuts is now the normal recommendation, especially for children at risk for an allergy.
Babies whose mothers ate more of a particular food during pregnancy or breastfeeding were more likely to prefer that food — flavors pass through both the placenta and breast milk. Randomized evidence shows that repeated exposure to a food increases a child’s liking of it, even for bitter vegetables. Kids are more likely to try foods with “autonomy-supportive prompts” and less likely with coercive ones like “If you finish your pasta, you can have ice cream.” Offer a wide variety; keep offering even if the child rejects them at first. The vast majority of allergies result from eight food types: milk, peanuts, eggs, soy, wheat, tree nuts, fish, and shellfish. The research is about regular exposure, not just one-time introduction — go slowly, one allergenic food per day, and work up to a normal amount.
Young children should have formula, breast milk, or water rather than juice; soda is strongly discouraged. Choking hazards — whole grapes, hard candies, nuts — are to be avoided; grapes are fine in pieces and nuts fine in nut-butter form. Cow’s milk as a primary drink is not recommended for infants — it is not a complete infant nutrition system, and infants who have it as their primary milk are more likely to be iron-deficient. Avoid honey through the first year of life due to the risk of infant botulism, a serious disease affecting breathing. Your toddler does not generally need a multivitamin; the main possible exceptions are vitamin D and iron, as vitamin D is not present in high concentrations in breast milk and many infants are considered deficient.
Chapter 13 — Early Walking, Late Walking: Physical Milestones
Pediatricians focus on three key milestone checkpoints. At nine months: rolling both ways, sitting with support, motor symmetry, and grasping objects. At eighteen months: sitting, standing, and walking independently. At thirty months: any loss of previous skills. The nine- and eighteen-month checkpoints are most crucial; by thirty months, most major issues have already been identified. There is enormous variation in when children hit milestones — walking alone ranges from 8.2 to 17.6 months; crawling, which 5 percent of kids never do, ranges from 5.2 to 13.5 months. Variation within these wide normal ranges is not a cause for concern.
Kids younger than school age get an average of six to eight colds a year, mostly between September and April, lasting an average of fourteen days — in the winter, your kid will have a cold roughly 50 percent of the time. 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 since they are caused by a virus. The move toward prescribing antibiotics sparingly is a good thing.
Chapter 14 — Baby Einstein vs. the TV Habit
Research shows that children under two cannot learn much from screens. Twelve-month-olds learned nothing from video demonstrations, and researchers trying to expose English-speaking infants to Mandarin via DVD found it did not work — a live person did. What matters for language development at this age is books — the most significant predictor of vocabulary size and growth was whether parents read to the child.
Slightly older children can learn from television. In the case of Sesame Street, good research suggests exposure increases school readiness in kids ages three to five, with bigger effects for children from more disadvantaged backgrounds. One study reported that watching more TV under age three lowered test scores by a small amount — about a couple of IQ points — but watching TV at older ages did not matter. The best evidence suggests TV watching even at very young ages does not permanently affect test scores. 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.
Chapter 15 — Slow Talking, Fast Talking: Language Development
The timing of language development has some link with later outcomes like test scores and reading, but the predictive power for any individual child is weak. Girls develop language faster than boys on average, though there is a lot of overlap. The key takeaway is reassuring: early talking does not guarantee later success, even at age four, and late talkers mostly look like everyone else within a few years.
Chapter 16 — Potty Training: Stickers vs. M&M’s
There are two broad approaches to potty training. 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, looking for signs of readiness. An eighteen-month-old is less likely to simply decide they will not poop in the potty no matter what — they have less will to defy you. A three-year-old can be reasoned with and bribed, but has more will to defy you.
The evidence suggests it is possible to train your child at a younger age if you adopt a more goal-oriented approach, or you can wait until they are closer to three. The child-led approach may take longer but may also be more pleasant. You will try anything — literally anything — to get your child to use the bathroom, but you cannot force them. Some kids respond to stickers, some to M&M’s. Potty training is really about what works for your family and your kid. Doctors generally do not worry about lack of nighttime dryness until a child is six years old.
Chapter 17 — Toddler Discipline
When you discipline a child for refusing to clean up a mess, it is not that you want help cleaning up — it is that you are trying to teach them to take responsibility for their messes now and in the future. Discipline is not the same as punishment. There is a punishment component, but it is in the service of raising better humans.
A number of evidence-based parenting interventions exist, including 1-2-3 Magic, the Incredible Years, and Triple P — Positive Parenting Program. For example, 1-2-3 Magic develops a system of counting in the face of disruptive behavior, with a defined consequence if three is reached. The emphasis is on consistency: whatever system you use, use it every time, and do not make threats you cannot carry out. Discipline should be reserved for actual bad behavior, not for things that are merely annoying. Research has found that spanking has negative long-term impacts on behavior problems — spanking at age one increased behavior problems at three, and at three increased them at five, even controlling for earlier behavior. There is no evidence that spanking improves behavior.
Chapter 18 — Education
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 open-ended questions: “Where do you think the bird’s mother is?” “How do you think the Cat in the Hat is feeling now?”
The three preschool philosophies most commonly encountered are Montessori, Reggio Emilia, and Waldorf. Montessori exposes even young children to letters, numbers, and counting. Reggio Emilia-inspired schools put more emphasis on play, with little formal letter or number exposure. Waldorf has a heavy outdoor component, is largely play-based, and includes a domestic activity component — cooking, baking, gardening. We simply do not have concrete data to guide you on which philosophy is best, and the best type may vary by individual child.
Chapter 19 — Internal Politics
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. Many people are still, on net, happy with their spouse. Just, slightly less.
Two specific factors play a role. The first is unequal chore allocation: women tend to do the bulk of household work even when they also work outside the home. The second is a decline in sex. Sleep is a key issue as well — drops in marital satisfaction are higher in couples whose kids sleep less. Lack of parental sleep contributes to depression in both parents and to less happy marriages.
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. These checkups seem to result in improvements in intimacy and marital satisfaction. Beyond this, there is other evidence in favor of therapy more generally — group couples therapy, counseling programs beginning before birth — focusing on communication and positive solutions to conflict.
Chapter 20 — Expansions
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 — likely reflecting more parental time invested in reading or skill development at young ages. The effects were pretty small.
The bulk of the evidence suggests there are some small risks, 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, and it may also just be easier on you as a parent given the intensity of the infant stage.
Chapter 21 — Growing Up and Letting Go
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.