DS is 21mo and only says Dadda and Mamma. He babbles incessantly but struggles with all the consonants: basically he doesn't move his mouth to form shapes. This is obvious because he can't do things like blowing which also reequire some mouth muscle movement. Also his 'Mamma' sounds like it's a huge effort with the kind of tone to it you'd expect from a deaf speaker.
His hearing and comprehension are perfect and he communicates well using signs, but we're worried about the lack of words! Whenever we encourage him to say things he hides his face and seems embarrassed.
Am I worrying needlessly? And what can I do to encourage him without him being embarrassed?
Any tips etc gratefully received! Thanks 