My DD2 was always a skinny minny - she would have been lucky to weigh 10kg at 1 and she finally got to 15kg by 4yo, and she looked so lean and skinny because she was tall but by the time she turned 5 she was 20kg. She put on 5kg in a year! I have no idea why the sudden growth spurt, she didn't eat any more than normal, but I guess her body just decided that it was the right time to grow. She is very nearly as tall as her older sister and they get confused for twins all the time.

DS2 is also a bean pole and I think he will follow DD2's growth pattern. When he was born there were 3 other boys born locally around the same time and though he was the biggest at birth (10lb1) come 12mths he was the smallest by far. One of the other boys' mums commented on how small he was in a really competitve tone and I just said 'yeah, better than being a fatso and having to worry about childhood obesity hey?" and she hasn't commented since. So as for comebacks to the 'gee they're small' comments it really depends on who said it and how it is said kwim? If someone is being competitive or trying to make him inferior simply because he is smaller, then I don't hold back, but if they are nice about it then it's just a 'yeah he is, but that's OK'