Lev Vygotsky's theory posited that cognitive and social development in children is the result of interaction between children and their social environment. He believed that play is an important form of socialization, as it allows children to shape their understanding of the world, develop thinking skills, and acquire language through imaginary conversations and imitation of others. Vygotsky also viewed play as essential for both language development and a child's comprehension of the external world, as it provides a context for children to talk through their experiences and make sense of the world.