sweetpea,
my bb is also quieter outside, then i realised its becos its a diff environment so there's a lot for him to watch and observe, so he becomes quieter. Once he is no longer as curious abt the new surroundings, he will start "talking" again.
qingling,
ur bb says other words so its ok lah. My bb also doesnt really call "mama" much, but he will give me a mischievous grin when i ask him to call me, so i know he understands, but is deliberately not calling me lor. I think as long as bb knows "mama" and "papa" shd be ok, unless bb really doesnt know who "mama and papa" refer to, then mabbe check with PD. I know a bb who is almost 2 yrs old and really quiet, doesnt really talk at all, only makes some sounds once in a while. Not even real words, and he is ok.