My 11 month old son has never babbled. He smiles a lot and makes some noise once in a while but he has never been a chatty baby. He understands some words like No, Dance, Give it to me etc. He only ever makes ba and ga sounds and when he is crying he makes ma sound. He is very active, crawls well and is almost standing up on his own without any support. Is this just delayed speech or should I be worried?