Early Childhood: Body and Mind

This is Unit Five, part one, on the body, brain, health and thinking of children from three to six. Unit Four closed on screens in infancy. Unit Five follows the child into the preschool years, from growth and health to a new way of thinking. Carry one question through this part: what can a preschooler's mind do, and what can it not do yet? A four-year-old turns a block into a phone, and insists the tall glass holds more juice. At the entry that puts preoperational thought together, the part answers: powerful and limited at once. By the end you will be able to tell experience-expectant from experience-dependent brain development. To explain what the Wakefield case teaches about research. To tell night terrors from nightmares. To describe preoperational thought. And to explain the false-belief task.

Three entries on growth from three to six: the numbers, what stunts it, and how boys and girls compare.

How children grow from three to six.

HGD 0601 Growth From Three to Six

From three to six, US children grow about two to three inches and gain four to five pounds a year, reaching about forty-five inches by six. A round-bellied three-year-old becomes a leaner six-year-old, as the head's share of body length keeps falling and the legs lengthen.

What limits growth.

HGD 0602 Stunting

Stunting is impaired growth in height, usually from malnutrition. It is not reversible, and it raises the risk of cognitive and physical damage. About one hundred forty-nine million children under five are stunted, more than a fifth worldwide, and rates reach nearly half in some poor parts of Africa and southern Asia.

Boys, girls, and growth.

HGD 0603 Boys, Girls and Growth

By four, boys average about three-quarters of an inch taller and two pounds heavier than girls, with more muscle, while girls carry more fat. But variation within each sex is far larger than the average difference between them.

Four entries on the brain: its size at six, two kinds of development, and the two hemispheres.

The brain at six.

HGD 0604 The Brain at Six

By six, a child's body weighs about thirty percent of an adult's, but the brain has reached about ninety percent of adult size, with dendrites two to three times as dense as the adult average. Growth comes from axons, dendrites and synapses, above all myelination; stress and poor nutrition slow it.

Two kinds of brain development.

HGD 0605 Experience-Expectant and Experience-Dependent

Brain development runs on two kinds of process. Experience-expectant processes are universal: the brain is primed for input nearly every child meets, such as patterned light and language, during sensitive periods. Experience-dependent processes reflect each child's particular experiences, such as learning a specific language or an instrument, and they continue across life. The distinction explains two kinds of risk. Missing expected input, sight or language, during a sensitive period can have lasting effects, as the cataract and orphanage cases showed. Missing a particular experience, such as music lessons, affects one skill, not the brain's basic organisation.

The brain's two hemispheres.

HGD 0606 Lateralization and Handedness

The left hemisphere typically handles language, and the right emotional expression, music and visual-spatial relations, but the hemispheres always work together. About ten percent of children, across cultures, prefer the left hand. The misconception is that people are left-brained or right-brained. No one thinks with one hemisphere alone.

Left-handed children.

HGD 0607 Left-Handed Children

About ninety-five percent of right-handers show typical lateralization, against about seventy-five percent of left-handers, and handedness reflects genes and environment together; it may appear by six months or not settle until nine. The misconception is that left-handers think or perform differently. No scientific evidence shows differences in cognition, art or athletics.

Six entries on health: food, sleep, night terrors, vaccines, a fraudulent study, and injury.

What young children need to eat.

HGD 0608 Nutrition in Early Childhood

Young children need carbohydrates for energy, proteins for tissue growth and repair, and fats for energy, vitamin absorption and brain development. A preschooler can be offered healthy choices and trusted to decide how much to eat. Food deserts, areas without ready access to fresh food, are linked to obesity, diabetes and heart disease.

How much preschoolers sleep.

HGD 0609 Preschool Sleep

The WHO advises about ten to thirteen hours of sleep a day for preschoolers, with consistent sleep and waking times; a four-year-old who drops naps may sleep longer at night. Short sleep is strongly associated with unhealthy weight gain, though family factors may confound the link.

Night terrors.

HGD 0610 Night Terrors

Night terrors affect about one to six and a half percent of children, peaking at five to seven. A child sits up screaming, sweating and thrashing, is hard to comfort, and remembers nothing next morning. The misconception is that night terrors are bad nightmares. Dreams occur in REM sleep; terrors come from deep sleep.

Vaccination.

HGD 0611 Vaccination

High vaccination coverage has nearly eliminated polio and measles in many countries, and there is no evidence that vaccines overburden the immune system. Global immunisation of children under five slipped from eighty-six percent in two thousand to eighty-three in twenty twenty-three. Case counts change year by year, so any figure must be dated to its source.

How one fraudulent study shaped vaccination.

HGD 0612 The Wakefield Case

In nineteen ninety-eight, Andrew Wakefield and colleagues published a study in The Lancet suggesting that the measles, mumps and rubella vaccine predisposed children to autism. It rested on twelve children, and its conclusions were speculative. It was later retracted, articles in the BMJ documented that the work was fraudulent, and Wakefield lost his licence to practise medicine. Before those corrections the claim spread, and vaccination rates fell. Here unit one's lessons meet real consequences. A sample of twelve cannot establish a cause; a correlation would not show cause either, and here the data were falsified. The case is not taught as a live controversy, because the science is not divided. It is taught because the safeguards, samples, replication and retraction, show their cost when a finding travels faster than its correction. The course takes no position on vaccination policy.

Injury in childhood.

HGD 0613 Injury in Childhood

After the first birthday, unintentional injuries are the leading cause of death in childhood, from fires, drownings and falls, with rates tied to socioeconomic status; differences across racial and ethnic groups follow those differences in status. Globally, diarrhoeal disease causes fifteen percent of under-five deaths, against under a tenth of a percent in the US.

Seven entries on motor skills from three to six, and on why movement matters for every child.

Motor milestones from three to six.

HGD 0614 Motor Milestones, Three to Six

Between three and four, children pedal a tricycle and copy a circle; by five or six, they skip, jump rope and write their names. A drawn person grows from two to four body parts at four to at least six by five. By middle childhood children move like adults, with less skill and strength.

Large movements, and precise ones.

HGD 0615 Gross and Fine Motor Skills

Gross motor skills use large movements such as running and hopping; fine motor skills use precise hand and finger movements, often guided by vision. Training wheels and a batting tee support immature judgement of trajectories and slower reactions. Both kinds grow with practice, which is why opportunity matters as much as age.

A disorder of coordination.

HGD 0616 Developmental Coordination Disorder

Developmental coordination disorder is a neurodevelopmental condition that impairs planning and carrying out coordinated movement, from tying laces to riding a bike: a child understands the rules of dribbling but cannot coordinate the movements. Early intervention helps both skill and self-esteem. The DSM-5-TR name is developmental coordination disorder, not dyspraxia.

Why movement matters.

HGD 0617 Why Movement Matters

Early physical activity is linked to healthier weight, cardiovascular fitness, higher bone density, and lower risks of diabetes, hypertension and some cancers. Active preschoolers show better attention and self-regulation, and later, better academic performance, and activity is linked to less depression, anxiety and stress, including among children with ADHD.

The WHO's activity guideline.

HGD 0618 The WHO's Activity Guideline

The WHO recommends that three- and four-year-olds spend at least one hundred eighty minutes a day active, including at least sixty minutes of moderate-to-vigorous activity, no more than an hour at a time in a stroller, and no more than an hour of sedentary screen time. These are the WHO's recommendations, reported here, not advice from the course.

Sex differences in motor skill.

HGD 0619 Sex Differences in Motor Skill

Girls show better fine motor skill and balance from about two; boys outperform in some gross skills needing speed or object control, such as catching. Parents give boys more rough-and-tumble play and girls quieter play, adding practice to any biological difference. The misconception is that boys are better at motor skills. Counted across all skills, differences may disappear.

Children with physical disabilities.

HGD 0620 Disability and Activity

Children with physical disabilities gain the same benefits from activity, in fitness, strength, coordination, mood and social skills, as other children, as a child in a wheelchair on an adapted playground shows. The barriers are practical and social: inaccessible facilities, missing adapted equipment, and attitudes toward disability.

Eight entries on thinking in early childhood, most of them on Piaget's preoperational stage. The opening question is answered here.

Early cognitive milestones.

HGD 0621 Early Cognitive Milestones

Typical milestones include knowing one's age and full name at four, counting to ten and retelling a story in order at five, and simple addition and subtraction at six. Three-year-olds vary widely, and malnutrition and emotional deprivation can impair the brain development these milestones depend on.

A famous study of language at home.

HGD 0622 The Thirty-Million-Word Gap

Hart and Risley reported that children in higher-income homes heard about thirty million more words by four, and vocabulary tracked that exposure. Later work questions the method and the figure. Language exposure and child-directed speech, not income itself, best predict later language.

Piaget's second stage.

HGD 0623 The Preoperational Stage

Piaget's preoperational stage runs from about two to seven. Pre means before operations, logical mental actions that can be reversed, as when a seven-year-old sees that three doubled and seven minus one both make six. Some sources end the stage at six; either way, concrete operations follow, from about seven.

Symbols, and a living world.

HGD 0624 Symbolic Representation and Animism

Preoperational children use symbolic representation, letting words and objects stand for other things, so a crayon flies as a rocket. They also show animism, believing objects are alive and conscious, like a child sure the moon is following her home. Symbolic thought drives imaginative play; animism fades as children learn how the world works.

Seeing only one's own view.

HGD 0625 Egocentrism and the Three Mountains

Egocentrism is difficulty separating one's own perspective from others'. In Piaget's three-mountains task, children pick the view a doll would see: a four-year-old chooses her own view, a seven-year-old the doll's. Moving beyond one's own viewpoint is called decentering, and later research finds perspective-taking earlier than Piaget believed.

One feature at a time.

HGD 0626 Centration and Conservation

Centration is attending to one feature at a time, which is why preoperational children fail conservation tasks, judging amount by a single dimension: poured into a taller, narrower glass, the juice looks like more. The misconception is tall glass, more juice. Conservation arrives with concrete operations, around seven.

The payoff: preoperational thought, together.

HGD 0627 Preoperational Thought

Preoperational thought, from about two to seven, is powerful and limited at once, and that answers this part's question. Symbolic representation lets words and objects stand for other things, fuelling pretend play. Animism attributes life and feeling to objects. Egocentrism makes it hard to take another's perspective. Centration fixes attention on one feature, so conservation tasks fail. The stage is named for what children cannot yet do, but its gains are real: symbolic thought is the foundation of language and imaginative play. And later research finds that preschoolers take others' perspectives earlier and more skilfully than Piaget's tasks showed.

Understanding other minds.

HGD 0628 Theory of Mind and False Belief

Theory of mind is understanding that other people have beliefs, desires and perspectives different from one's own, and it is often tested with the false-belief task. A child watches a character put a ball in a basket and leave; a second character moves it to a box. Asked where the first character will look, children with theory of mind say the basket, where the character wrongly believes it is. Most pass at about four or five; a three-year-old points to the box. Theory of mind has several parts on different timelines, and children with older siblings tend to pass earlier.

Look at what you can now do. You can tell experience-expectant development, primed for input nearly every child meets, from experience-dependent development, shaped by each child's particular experiences. You can explain what the Wakefield case teaches: twelve children cannot establish a cause, the data were falsified, the study was retracted, and distrust outlived the correction. You can tell night terrors, from deep sleep and forgotten by morning, from nightmares, which come in REM sleep. You can describe preoperational thought: symbolic representation, animism, egocentrism and centration, powerful and limited at once. And you can explain the false-belief task: a child with theory of mind says the character will look where she wrongly believes the ball is. Part two covers what stays fixed in Piaget's stages.