Studies here trying to identify causes of childhood obesity point to * children being driven to school (no longer walking), * 'stranger danger' fears dissuading parents from letting their children play out * school authorities selling off playing fields to raise cash
On top of the stuff about the internet and television..
Myself, I can't help but think that the problem is mostly overstated. Sure, some kids are a bit tubbier than we were, but when I went to school, children were all super skinny, and hungry all the time.
(Western societies have only started to get used cheap food. When my mother taught in Bradford, West Yorks. in the seventies, there were still children with ricketts from undernourishment. There is bound to be some adjustment to cheap and abundant food. I am still amazed to see children leave food on their plates - I would never had done that as a child)