My g-grandmother was 5'11"+, other than that, the women on my Mothers side tend more to be shorter than 'average'. The women on my dad's side tend more to be shorter than 'average'. EVERYONE on my husband's side tends to be short for their age&sex. This is genetics... I am not surprised that my children are short for their age. Their BMI is in line with normal because unhealthy drinks and food are a treat rather than a 'regular snack/meal'. Sodas and chips are an easy way out to give snacks and are all too often much too available in homes. It's not a rare occurance to see 'the fat family' at the local store. I don't understand people that don't want better for their children. The parents likely suffered taunting and abuse as children because of their weight (and their parents' lack of control). Why don't they provide better so that their children don't have to live that way?? I try to keep my bad habits away from my children... Unhealthy chips, cookies, ice cream etc. are for after they are in bed. It costs extra to buy low fat, low sugar, 'healthy' junk food that they get on weekends. (Sugar DOES effect their behavior - I wish I had the moment I realized it 100% on video)
You're right that genetics make a big difference. But I think that most of us can tell if a child is naturally small (or large), or is very under- or overweight.
I do think most parents do want the best for their children, but some of them are awfully ignorant about good nutrition. Schools used to teach courses on nutrition, but I don't think that's so common anymore.
My neighbor has absolute proof that sugar affects behavior. She has 10 grandchildren under the age of 7. They are usually very well-behaved children. A couple of months ago, they had a birthday party that they taped. The kids, who normally don't get sweets, all had cake, ice cream and sodas. They went nuts - you can see on the video when the "sugar rush" kicked in. :-)
I sometimes wonder if many of the kids who are drugged with things like Ritalin are really just victims of a bad diet. I think it would be nice if we could find a way to educate parents so that kids get good nutrition, but my anti-big gov't tendencies make it hard. Schools seem to be the least intrusive way to do it, and now that we have schools pushing Ritalin, etc., maybe looking at diet first isn't too far to go.