Infancy and Childhood

From birth to roughly the start of puberty — a long stretch of rapid growth and the steady building-out of the body and brain.

What is happening

• Physical growth — children grow faster in the first year than at any later point; height and weight then climb steadily.
• Brain development — the brain reaches most of its adult size early, while connections between neurons are formed, strengthened, and pruned at an enormous rate.
• Motor skills — control develops in a predictable order, from head to toe and from the body’s center outward: holding the head up, sitting, crawling, walking.
• Immune learning — a newborn’s immune system is inexperienced; each infection and vaccination teaches it to recognize a new threat.

Why it matters

The body and brain are unusually plastic in childhood — highly shapeable by experience, nutrition, and environment. This makes childhood both a window of great opportunity and a period of real vulnerability.