Rachel,
my boy is a small bb too, @ 12 mths he only weigh 8kg, furthermore, he has milk strike recently for almost 3 weeks, cannot finish a bowl of porridge like he use too and now having flu on med. finally this morning hear him crying for milk and he can only drink at most 5oz. Also, finally see 2 more bottom tooth coming out.
but as long as he eat, play well and healthy, i'm not so concern.