I wouldn't worry too much, my twin boys are 14mths next week and my DS2 still only says mumma, DS1 will say mum, dad, bye bye (but only when he wants) but he babbles a lot...

They don't have the same language skills as DD at the same age, but they are more developed in their motor skills - I just think boys are more about doing whereas girls are more articulate. We never use baby talk and will always acknowledge anything they are playing with ie: Do you have a book, is that a car etc.

Saying that they do understand what is said to them and they are able to communicate in their own way their basic needs, so they will get the talking thing in their own time