My Ardyn is about the same age as your Lily, and she is the same. Pretty slim all over, and has this belly out in front. Not chubby, just protruding. It's not rel noticeable in clothes, but definitely when she's undressed. DH made a comment the other day that she eats too much and could be overweight......no way! Her weight is in perfect proportion to her height.

I've always assumed that it'd go away as her stomach muscles became stronger.