Dear Lonelady and Movenpick,
I once read an article on delayed speech development, and it mentioned that in a lot of cases, the delay is due to a hearing impairment. Meaning which, if a person cannot hear you, how can they respond? So intervention is first of all, to rule out whether they have a hearing problem. Secondly, they will see if the mouth and tongue is properly developed. In some cases, they have weak muscles, which means they cannot speak clearly - but not due to the lack of trying. For this, usually speech therapy would be recommended.
So, Lonelady, you should get that assessment asap, because your girl has not been repeating what she hears. Unless you know for sure, she can hear you and understand you. Whereas, for Movenpick, can wait a few more months, because we know hearing isn't a problem. And it seems like he is speaking, too! However, for children, they need to like you before they would learn from you. So, perhaps some activities that they like, like singing, dancing, watching TV together, etc might help to bring out the speech in them. Unfortunately, most maid prefers our children to be quiet and don't engage them to talk. I made the same mistake with my second child, too. He didn't speak or sing till quite late. Again, playgroup was a big help.
In many cases, when us as parents observe our children, we kinda know whether they are just taking their time, or perhaps there is a nagging feeling that something is wrong. I recall once I was busy washing the floor, and my son came to me with a packet of snacks. So I told him, wait, mama is washing. hands dirty. When mama is done, I open for you ok? sit here and wait. So he waited, and of course I forgot... but after keeping the pails and the broom and I turned around, there he was, with the snack in hand, big smile on his face. So he understood! And understanding is a big part in communication!!