This document discusses theories of cognitive development and language development. It covers Piaget's stages of cognitive development including the sensorimotor stage, preoperational stage, concrete operational stage, and formal operational stage. It also discusses Vygotsky's sociocultural perspective including concepts like the zone of proximal development and scaffolding. Finally, it addresses language development and compares the theories of Piaget and Vygotsky, outlining key differences in their views.