Watch a toddler for an afternoon and you'll see a scientist at work: dropping things to see what happens, hiding and finding toys, and slowly figuring out that other people have minds of their own. Developmental psychology studies how that thinking grows.
Piaget's stages
Jean Piaget, a Swiss psychologist, spent decades watching children solve problems. He proposed four stages:
- Sensorimotor (birth to 2). Babies learn through their senses and movement. A key milestone is object permanence, knowing a toy still exists under a blanket.
- Preoperational (2 to 7). Children use words and pretend play, but struggle to see things from another point of view, which Piaget called egocentrism. They also fail conservation tasks: pour water into a taller glass, and they'll say there's more.
- Concrete operational (7 to 11). Logical thinking about real, concrete things arrives. Conservation makes sense now.
- Formal operational (11 and up). Abstract thinking and reasoning about hypotheticals.
Later research suggests Piaget underestimated young children: with simpler tests, babies show some of these abilities earlier. Development also looks less like neat steps and more like gradual change. But his core idea, that children think differently from adults rather than just knowing less, has lasted.
Learning with help
Lev Vygotsky stressed the role of other people. His zone of proximal development is the space between what a child can do alone and what they can do with help. Good teaching gives just enough support (scaffolding) and then gradually takes it away.
Understanding other minds
Around age 4, most children develop theory of mind: understanding that other people can believe things that aren't true. In the classic Sally–Anne test, a 3-year-old usually says Sally will look for her marble where it really is; a 4- or 5-year-old knows she'll look where she left it.
Attachment
John Bowlby argued that a reliable bond with a caregiver gives a child a secure base to explore from. Mary Ainsworth's Strange Situation procedure watches how toddlers react when a caregiver leaves and comes back, and is still used to study attachment styles.
Try it
The cards below cover Piaget's stages, theory of mind, attachment and the nature–nurture question.