The document discusses key concepts and theories related to child development from several influential psychologists and researchers. It covers Piaget's stages of cognitive development including sensorimotor, preoperational, concrete operational, and formal operational stages. It also discusses Vygotsky's sociocultural perspective on development and the role of social learning and the zone of proximal development. Finally, it notes some limitations of Piaget and Vygotsky's theories, including inconsistencies in Piaget's stage theory and the underestimation of children's abilities.