My son is six months old. He was born at 36 weeks. He sits with support. Recognize family members. Roll overs both side I. E. Front to back and back to front. Smiles when anyone calls him. Even laughs when we make him laugh. But he doesn't make any sound when we talk to him. When we talk to him he blows raspberries. When he plays on his own he babbles some time. My concern is why he doesn't makes sound when we talk to him.