Jean Piaget's cognitive development theory explains how children develop their thinking skills through four stages. These stages are sensorimotor, preoperational, concrete operational, and formal operational. Each stage represents a different way of understanding the world, starting from basic sensory experiences to more complex abstract reasoning. In the sensorimotor stage, infants learn through their senses and actions. The preoperational stage involves symbolic thinking but lacks logical reasoning. During the concrete operational stage, children begin to think logically about concrete events. Finally, in the formal operational stage, adolescents develop the ability to think abstractly and systematically.