I co-sign Cutiepie2000's post on physical activity needing to start early.
I think most of the problem stems from the parents, which in turn stems from society. It's this ingrained "instant gratification" society that is at the root of the issue. People want things now: fast food, convenience stores, TV, video games, etc. And in exchange for rapid service and bigger quantity, society gets lesser quality, of food and life, which affects it as a whole.
Yes, there are other uncontrollable factors involved, including genetics, but if you know you're predisposed to something, be proactive about it! Obesity is a disease, why should it be treated any differently from any other genetically influenced disease? We as a society know the risk factors, why aren't precautions taken? I don't understand how parents who were overweight themselves as children can raise their children in the same way and perpetuate a cycle that they know is both unhealthy and emotionally damaging.
Our bodies were not made to sit in front of a TV all day, drinking Coke and eating crisps, rather (in an evolutionary sense), we were made for work. But now that culture has gone past the point where we had to physically exert ourselves to get food, we haven't kept up with what our bodies need.
My parents started me off early. I was in ballet by the time I was 3 years old, and had been running around and swimming before that. I didn't get to watch too much TV, and there was never any junk food around the house. I didn't have pizza until I was 15, by the way. (I know my case is a little extreme).
But I was healthy, and happy and the good diet and exercise equalled positive self-esteem for me. I'm about average sized, by the way (size 6-8), a little smaller during heavy dancing periods.
To sum up my oratorical fireworks, I think it's up to the parents to make the change. It has to be drastic, and it has to be permanent, because if they leave it up to someone at a school or camp, when the kid comes back home, they're just going to slip back into old habits, because it's comfortable.
~ShyViolet