According to Lev Vygotsky –

Correct Answer: language plays an important role in cognitive development of children.

Lev Vygotsky was a seminal Russian psychologist best known for his Socio-Cultural Theory of Cognitive Development. According to Vygotsky, cognitive development is fundamentally a social process deeply embedded in cultural and social interactions.

A central tenet of Vygotsky's theory is that language plays an indispensable role in cognitive development. Language serves two crucial primary functions for children:

1. Social Communication: It allows children to interact with adults and more knowledgeable peers, through which cultural tools, knowledge, and problem-solving strategies are transmitted.
2. Self-Regulation and Thought: Language transforms into an internal tool for thought. Vygotsky described how private speech (talking to oneself out loud) gradually becomes internalized into inner speech, guiding a child's mental processes, self-regulation, and reasoning skills.

Explanation of Incorrect Options:

• "children learn language through a ‘language acquisition device’" refers to Noam Chomsky's nativist theory of language development.
• "children’s cognitive development occurs in stages" and "maturation of schemas leads to cognitive development in children" are core concepts of Jean Piaget's cognitive development theory, not Vygotsky's.