My almost 15 month old has only gained 2 oz's since the begining of November..?

My daughter has not gained any weight in quite some time. She turned 2 in December and only weighs 23 pounds (less than her 11 month old brother, and her twin brother is 10 pounds heavier)... She still can wear 12 month pants, but they are to short. I have to buy 18 month pants and take the waist in unless they have the adjustable waist. She is just going to be a petite girl and it sounds like your daughter is too.