My baby is 9 months and 10 days old. He is very active and playful. Always smiling and laughing. He interacts well with us. But he doesn't make the consonant babbling sound yet. I know he can make them as I have heard him say mah, bah, gah like sounds before. But on a regular basis he doesn't make sounds like ba-ba or ma-ma. When playing with him, I try to teach him how to make those sounds. He keenly observes but doesn't copy them. Is this a delayed milestone ? should I be worried?