The document discusses four main theories of language development in children: behavioral theory, nativist linguistic theories, social interactionist theory, and cognitive theory. Behavioral theory views language as learned through conditioning and environment. Nativist linguistic theories propose an innate language acquisition device. Social interactionist theory emphasizes the social environment and context. Cognitive theory, proposed by Piaget, sees language developing through cognitive maturation stages. Overall, the document examines the key theories but notes language development remains complex with no single theory providing a full explanation.