Sorry if I am being a thread-hogger here, it's just a very interesting subject.
I just wanted to add, to all of my other points, that there is an assumption that is often made - not by anyone here, but in the "real world" - that "skinny" is the same as "healthy."
It is clear from many posters descriptions of their kids that a childs' shape seems to have no bearing on how sporty they are or how well they eat. In fact, reading back, most posters here talk about their "larger" child being the most active one.
I know plenty of adults that are super-skinny and yet eat rubbish. There is no way that they can be healthier than a larger person who eats well. Is it the same with children, or are we conditioned to think that "fat" children are unhealthy, regardless of their diet, while thin children are ok, even if they eat nothing but sweets?
Now I am aware of the health risks that come with being very heavy, and I am not talking about the super-obese adults and children, who clearly need to make changes in their lives.
But if a child is active and eats a balanced diet, then does it really matter if they are the largest in their class? Should we be looking instead at their super-twiggy classmates who eat only crisps and drink only Dr Pepper? (I know one sven year old just like that, I wonder how they will look in 10 years time)