My son of 19months, is not speaking yet. however He used to speak Baa...Baai...Taayi...Bhaiya....Koko...tutu...hatt..etc...but still he doesn't speak Mamaaa, papa..he doesn't call me mumma, and doesn't call his papa as papa...he calls baa to all...and if someone stranger comes at home, he doesn't speak a single word. and these things he is doing since last 6 months. now I am worried, that is he delayed in speaking as children of his age are speaking very good . please suggest ..