Piaget's Cognitive Development Theory is a comprehensive framework that explains how children's thinking evolves through distinct stages as they interact with their environment. This theory emphasizes the idea that children are active learners who construct knowledge through experiences, and it identifies four key stages of cognitive development: sensorimotor, preoperational, concrete operational, and formal operational. Each stage represents a different way of thinking and understanding the world around them, influencing their physical, cognitive, and social-emotional growth.