This document summarizes the cognitive development of preschoolers. It discusses Piaget's stages of preoperational thought, brain development, language development including fast mapping and scaffolding, information processing including attention and memory, theory of mind, receptive language skills, pre-reading and pre-math skills like matching, copying letters and numbers, attention and activity levels, concept formation, cause and effect relationships, episodic and semantic memory, logical reasoning, planning and organizing, creative thought, cognitive flexibility, and the role of caregivers in cognitive development for children ages 3 to 5 years old.