This document discusses Jean Piaget's theory of cognitive development. It outlines the four stages of development: sensorimotor, pre-operational, concrete operational, and formal operational. The sensorimotor stage occurs from birth to age 2 as infants learn through senses and motor skills. From ages 2 to 7, the pre-operational stage involves pretend play and egocentric thought. Concrete operational children from 7 to 11 can think logically about concrete ideas. Finally, formal operational stage from age 12 involves abstract reasoning and hypothetical thinking. The document provides details on characteristics of each stage and Piaget's contributions to understanding child intelligence development.