Nobody did! You merely said that a shirt provided for a 7 year old was still too large for a 10 year old. Yes, kids do vary in size, but the general impression your post gave (or at least the way I read it) was that the club hadn't quite got its sizing right.
Odd. I'm pretty much pro club re: this thread in general, but as far as the scheme is concerned, I'd have thought someone at the club would have a reasonable idea of the size of an average 7 year old.