In early childhood as in infancy, the body and brain develop according to powerful epigenetic forces—biologically driven and socially guided, experience-expectant and experience-dependent. (Developmental Link: Experience-expectant and experience-dependent brain development are explained in Chapter 5.) During this period, bodies and brains mature in size and function.

Compare an unsteady 24-month-old with a cartwheeling 6-year-old. Body differences are obvious. Height and weight increase greatly in those four years (by about a foot and 16 pounds, or almost 30 centimeters and 8 kilograms), but that is not the most remarkable change. During early childhood, proportions shift radically: Children slim down as the lower body lengthens and fat turns to muscle.

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In fact, the average body mass index (BMI, a ratio of weight to height) is lower at ages 5 and 6 than at any other time of life. (Developmental Link: Body mass index is defined in Chapter 11.) Gone are the infant’s protruding belly, round face, short limbs, and large head. The center of gravity moves from the breast to the belly, enabling cartwheels, somersaults, and many other motor skills. The joys of dancing, gymnastics, and pumping a swing become possible; changing proportions enable new achievements.

New shape and ability occur as weight and height increase. Over each year of early childhood, well-nourished children grow about 3 inches (about 7½ centimeters) and gain almost 4½ pounds (2 kilograms). By age 6, the average child in a developed nation:

When many ethnic groups live together in a nation with abundant food and adequate medical care, children of African descent tend to be tallest, followed by those of European, then Asian, and then Latino descent. However, height differences are greater within ethnic groups than between groups, evidence again that ethnic differences are not primarily biological.

Although they rarely starve, preschool children sometimes are malnourished, even in nations with abundant food. The main reason is that small appetites are often satiated by unhealthy foods, crowding out needed vitamins.

Adults often encourage children to eat, protecting them against famine that was common a century ago. Unfortunately, that encouragement is destructive in almost every nation. For example 30 years ago in Brazil, the most common nutritional problem was undernutrition; now it is overeating (Monteiro et al., 2004). Low-income Brazilians are particularly vulnerable, but even wealthy Brazilians eat a less nutritious, higher calorie diet than they did a few decades ago (Monteiro et al., 2011).

In developed nations, children or grandchildren of immigrants are more likely to ingest inadequate amounts of healthy food than their elders who were born elsewhere (de Hoog et al., 2014). Further, the rate of poor nutrition increases as family income decreases; the same is true of obesity. Childhood obesity is not simply a problem in itself, it is also a marker of poor nutrition, and likely to reduce the functioning of the immune system lifelong (Rook et al., 2014).

There are many explanations of the increasing obesity as income falls. One is that many low-income children live with grandmothers who knew firsthand the dangers of malnutrition. They reward children with sweets, and they foster other eating patterns that combat starvation that no longer is a problem. They do not realize that traditional diets in Latin America or Africa are healthier than current foods advertised to children on television (de Hoog et al., 2014).

Of course, mothers and fathers also contribute to childhood obesity. Many family habits—less exercise, more television watching, fewer vegetables, more fast food—are more common in low-SES families than in those with wealthier, more educated parents (Cespedes et al., 2013).

Caregivers need to realize that appetite decreases between ages 2 and 6 because young children grow more slowly and need fewer calories per pound than they did as infants. This is especially true for the current generation, who burn fewer calories because they are less active compared to children fifty years ago. Once most children lived in rural areas where they played outside all day. Instead of adjusting to this ecological change, many adults fret, threaten, and cajole children to overeat (“Eat all your dinner and you can have ice cream”).

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Many developmentalists promote more exercise in children. Such efforts are not always successful, as is evident from a study of many Latin American nations (Barboza, 2013). (Developmental Link: Obesity and exercise are discussed in Chapter 11.) There is good news in the United States, however. Obesity among preschoolers has declined slightly in recent years. It still is far too high (about 12 percent) but a combination of public education and parental action has led to improvement (MMWR, January 18, 2013; MMWR, August 9, 2013).

Although many young children consume more than enough calories, they do not always obtain adequate iron, zinc, and calcium. For example, North American children now drink less milk than formerly, which means they ingest less calcium and will have weaker bones later on.

Eating a wide variety of fresh foods may be essential for optimal health. Compared with the average child, those preschoolers who eat more dark-green and orange vegetables and less fried food benefit in many ways. They gain bone mass but not fat, according to a study that controlled for other factors that might correlate with body fat, such as gender (girls have more), ethnicity (people of some ethnic groups are genetically thinner), and income (poor children have worse diets) (Wosje et al., 2010).

Sugar is a major problem. Many customs entice children to eat sweets—in birthday cake, holiday candy, desserts, and other treats. Sweetened cereals and drinks (advertised as containing 100 percent of daily vitamins) are a poor substitute for a balanced, varied diet, partly because some nutrients have not yet been identified, much less listed on food labels. The lack of micronutrients is severe among people in poor nations, but vitamin pills and added supplements do not always help (Ramakrishnan et al., 2011).

Within the United States, children of all ethnicities drink more sweetened beverages than they once did, a problem particularly common among African Americans (de Hoog et al., 2014). They have a higher incidence of lactose intolerance, so they may avoid drinking milk. However, that may needlessly reduce nutrition. Most African Americans can digest some milk, and yogurt is a good calcium source if children are truly upset by lactose (Marette & Picard-Deland, 2014). However, yogurt is expensive and non-traditional, so parents need to be aware that yogurt drinks are far better for children than drinks with sugar or corn syrup.

An added complication is that an estimated 3 to 8 percent of all young children are allergic to a specific food, almost always a common, healthy one: Cow’s milk, eggs, peanuts, tree nuts (such as almonds, walnuts, etc.), soy, wheat, fish, and shellfish are the usual culprits. Diagnostic standards for allergies vary (which explains the range of estimates), and treatment varies even more (Chafen et al., 2010).

Some experts advocate total avoidance of the offending food—there are peanut-free schools, where no one is allowed to bring a peanut butter sandwich for lunch—but other experts suggest that tolerance should be gradually increased, beginning by giving babies a tiny bit of peanut butter (Reche et al., 2011). Indeed, exposure to peanuts can begin before birth: A study of pregnant women who ingested peanuts found that their children were less likely to be allergic (Frazier et al., 2014). Fortunately, many childhood food allergies are outgrown, but since young children are already at nutritional risk, allergies make a balanced diet even harder.

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Yet another complication is that many young children are compulsive about daily routines, insisting that bedtime be preceded by tooth-brushing, a book, and prayers—or by a snack, sitting on the toilet, and a song, in that order. My grandson always wanted a story, but not just any story. He told me it had to be a made-up story about an animal that has a problem that is solved by the end of the story. Thankfully, despite such very specific criteria, his literary standards were low, so I could comply. Whatever the routine, children expect it and are upset if someone puts them to bed without it.

Fortunately, as a team of experts contends, “Most, if not all, children exhibit normal age-dependent obsessive-compulsive behaviors [that are] usually gone by middle childhood” (March et al., 2004, p. 216). Parents need to balance their concern for good nutrition with the child’s normal wish for sameness. This is another reason a variety of healthy foods, including some that may not be the family’s usual fare, need to be fed early in life, before the child develops antipathy to particular fruits or vegetables.

Not surprisingly, tooth decay correlates with obesity; both result from a diet with too much sugar and too little fiber (Hayden et al., 2013). More than one-third of all U.S. children under age 6 already have at least one cavity (Brickhouse et al., 2008). Sugary fruit drinks and soda are prime causes, and sugar-free soda contains acid that makes decay more likely (Holtzman, 2009).

“Baby” teeth are replaced naturally at about ages 6 to 10. The schedule is primarily genetic, with girls a few months ahead of boys. However, tooth care should begin years before the permanent teeth erupt. Severe tooth decay in early childhood harms those permanent teeth (which form below the first teeth) and can cause jaw malformation, chewing difficulties, and speech problems. The United States Preventive Services Task Force (a panel of experts in evidence-based medicine) urges pediatricians to add fluoride coats to the teeth of preschoolers who have no other source of fluoride, as that is proven to reduce cavities (Moyer, 2014).

Teeth are affected by diet and illness, which means that the state of a young child’s teeth can alert the doctor or dentist to other health problems. The process works in reverse as well: Infected teeth can affect the rest of the child’s body.

Most preschoolers visit the dentist if they have U.S.-born, middle-class parents; however, the less education parents have, the less likely they are to know the importance of early dental care (Horowitz et al., 2013).

If the parent was raised in a nation with inadequate dental care (sometimes evident in the number of toothless elders), they may not schedule dentist visits for their children or insist on tooth brushing. However, in many countries ignorance is not the problem; access and income are. In the United States, free dentistry is not available to most poor parents, who “want to do better” for their children’s teeth than they did for their own (Lewis et al., 2010).

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