The problem is that what is considered normal, is not. And most of those children who enjoy a "normal childhood" will be obese and diabetic in the future. And it's great to eat shit and be skinny ... until your genetics decide that's enough. We had all been 15 years old and we know that calories are not stored at that age the same as when you are 30 years old. Even being active, imagine when your are sedentary.
20 or 30 years ago, when most of us here were young, we had limited access to sweets, pizza, coke, chocolate, etc ... At leat I had.
What I mean is that you must understand that taking care of your body and heath is not a sacrifice, it is something beneficial. Finding the middle ground is not easy, but a minor cannot make rational decisions (well, there are minors who are much more rational than most adults, but you get the point), so having them in a "normal environment" where there are so many addictive foods is a recipe for disaster.
I don't know what the solution is, I don't have kids and I would never have them in such an unhealthy environment, it's not a problem I have to deal with. But most parents should not have children, just how they are feeding himself and they kids, it is a disaster.