Cognitive development theory, primarily associated with Jean Piaget, explains how children develop thinking and understanding as they grow. Piaget proposed that children progress through four stages: sensorimotor, preoperational, concrete operational, and formal operational. Each stage represents a different way of thinking and interacting with the world. This theory emphasizes that children actively construct their knowledge through experiences and interactions. As they encounter new information, they adapt their existing mental frameworks, a process known as assimilation and accommodation. Understanding these stages helps educators and parents support children's learning and cognitive growth effectively.