For a great discussion of why kids and the rest of us are fatter today than in the past, see this article by Professor Dwight Lee in the latest issue of the Intercollegiate Review, a publication of the Intercollegiate Studies Institute.  His points out that we have gone from a society that in the past has had starvation as a major worry to one where one of our biggest concerns is being overweight. But he concludes that this is not a problem but a success story attributable to freedom.