Piaget proposed four stages of cognitive development: Sensorimotor, Preoperational, Concrete Operational, and Formal Operational. The concept of Post-Formal Operational stage was not proposed by Piaget.

In the Sensorimotor stage, infants learn about the world through their physical interactions and sensory experiences. They explore objects, manipulate them, and learn about their properties through touch, taste, smell, sight, and hearing.

Egocentric thinking is a characteristic of the Preoperational stage. Preoperational children believe that everyone sees the world the same way they do and have difficulty understanding other people's perspectives.

Piaget's theory of cognitive development is primarily based on his observational studies of children's behavior. He observed children's interactions with their environment and how they learned and developed over time.

During the Concrete Operational stage, children develop the ability to reason logically about concrete objects and events. They can understand cause-and-effect relationships and perform simple mathematical operations.

Hypothetical-deductive reasoning is a characteristic of the Formal Operational stage. Formal operational children can formulate hypotheses and test them systematically to solve problems and draw conclusions.

One criticism of Piaget's theory is that it underestimates the cognitive abilities of young children. Some researchers argue that young children are more capable of abstract thought and logical reasoning than Piaget believed.

Object permanence is a key concept in the Sensorimotor stage. Sensorimotor children develop the understanding that objects continue to exist even when they are out of sight.

Piaget's theory of cognitive development has been influential in the development of educational curricula and teaching methods, the design of toys and games for children, and the understanding of child psychology and development.

Animism is a characteristic of the Preoperational stage. Preoperational children often attribute human characteristics to inanimate objects, such as believing that toys have feelings or that the wind is a person.

Piaget's theory of cognitive development has been used to explain the development of language, moral reasoning, and mathematical abilities in children.

Conservation of mass is a key concept in the Concrete Operational stage. Concrete operational children develop the understanding that the amount of a substance remains the same when it changes shape or appearance.

One criticism of Piaget's theory is that it ignores the role of culture and society in cognitive development. Some researchers argue that culture and society play a significant role in shaping children's cognitive development.

Hypothetical-deductive reasoning is a characteristic of the Formal Operational stage. Formal operational children can formulate hypotheses and test them systematically to solve problems and draw conclusions.

Piaget's theory of cognitive development has been influential in the development of educational curricula and teaching methods, the design of toys and games for children, and the understanding of child psychology and development.