Cognitive Development Theory, proposed by Jean Piaget, explains how children develop thinking and understanding as they grow. Piaget identified four stages: sensorimotor, preoperational, concrete operational, and formal operational. Each stage represents different ways children perceive and interact with the world, progressing from basic sensory experiences to complex abstract reasoning. The theory emphasizes that children actively construct knowledge through experiences and interactions. As they encounter new information, they adapt their existing mental frameworks, a process known as assimilation and accommodation. This ongoing development shapes their ability to think critically and solve problems throughout life.