What are Piaget's four stages of cognitive development?

Jean Piaget proposed four stages. The sensorimotor stage from birth to about age two, where infants learn through senses and motor actions and develop object permanence, the understanding that objects continue to exist when out of sight. The preoperational stage from two to seven, where children develop language and symbolic thinking but lack conservation and are egocentric. The concrete operational stage from seven to eleven, where children master conservation, classification, and logical thinking about concrete events.