The core of Piaget's theory is "genetic epistemology". He believes that human knowledge comes from action, which is the source of perception and the basis of thinking. The essence and reason of children's psychological development is that the subject adapts to the object through action. On the basis of the existing schema, children's cognition develops from low to high through assimilation, adaptation and balance.

Piaget s theory of stages of cognitive development;

1. Sensory motor stage (0-2 years old): Stage characteristics: differentiation of sensation and movement; Eternity of object; The ability to solve problems began to develop; Delayed imitation production.

2. Preoperative stage (2-7 years old): Stage characteristics: early signal function; Self-centeredness; Thinking is irreversible; Animism; Do not have the ability of logical thinking

3. Specific operation stage (7- 1 1 year): stage characteristics: self-centered; Thinking is reversible; Conservation; Can be classified; serialize

4. Formal operation stage (1 1- adult): able to infer the relationship between propositions; Ability to conduct hypothesis-deductive reasoning and analogical reasoning; Thinking is reversible and compensatory; Have the ability to reflect; Flexible thinking; Have abstract logical thinking