I also have a little tiny girl. She's 7 and still wears size 5 (just going into a 6) clothes, she's the smallest child in the whole school and when people see her in her uniform they think she's playing dress up lol. My nephew is a year younger than her and has always been bigger, in fact my sister gives me some of his old clothes for her to wear, we joke about them being 'hand me ups'.

Seriously, don't let them get to you. You could use the good old 'good things come in small packages' line or get them to focus on her positives like how she was walking at 9 mths.

As long as she's happy healthy and LOVED nothing else matters.