1) The document discusses Jean Piaget's theory of cognitive development, which he divided into 4 main stages: sensorimotor, preoperational, concrete operational, and formal operational.
2) Each stage is characterized by different types of thought processes and ways of understanding logic and the world. The preoperational stage involves intuitive and preconceptual thought, while the concrete operations stage involves more logical and reversible thought.
3) Key concepts in Piaget's theory include assimilation, accommodation, and equilibration to describe how children incorporate new information and experiences into their existing understanding through active experimentation.