My son is 3 years old. He is physically grown and active in all activities. But the main problem is he does not speak in normal conversation, he can identify all words and could spell them even he remembers A to Z and 1 to 20.Many times he is not actually aware that we are calling him and he remains busy with in himself. He can spell out basic words like papa mummy but either he calls both of us papa or mummy. Rest he can ask for water or about poty or if he wants to eat anything. But he generally don't talk to us the way children of his age do. Sir please guide us what should we do?