Still Won't Say "Ma Ma"

Ian is saying all kinds of things. For example, he will say "up", "uh oh", "da da", "bah" (for our dog), but still refuses to say "ma ma". He added a new word today.... "hi" and he actually strung together two words and said "hi da"...that is right, when Scott walked in the room Ian actually said "hi da". He greeted his father! He won't even say "ma", but he will greet his daddy upon entering the room. I know the boy loves me, and maybe he is just holding out for the perfect time to spring it on me, but I really am ready to hear him say "ma ma"!