Well for one, back in the 'good ole days' parents didn't just allow their kids to sit on the couch and eat potato chips all the time while they were home. There were chores to be done, dinner to be cooked, dishes to be done, yards to mow, pecans to pick up, animals to feed, eggs to gather, etc. The kids were just asked to help, it was demanded of them to help. In doing this they had less time for vegging out on the couch all weekend. Instead, most 11 yr olds would be out mowing lawns for some spending money early in the morning, or they would be running paper routes on their bikes. They were burning calories and earning money at the same time. The girls would babysit younger children, or go clean an elderly person's house for them, again for spending money.
Nowdays, we find 11 yr olds sitting on couches across America playing on the playstation and shoving cheetos in their mouths by the handful while we cry out that having children earn money is cruel and unusual.
Parents have given their children this crutch that the child shouldn't have to do anything and that the child is entitled to everything. This is entirely backwards thinking.
Part of it is the school's part for allowing ice cream and soda machines in their schools in the first place, school's know children can't control themselves when it comes to sweets. They are also partially to blame when funding gets cut and PE and academia suffer but the athletics department continues to receive funding. Not every child is going to participate in athletics, but that shouldn't mean the child should be fat and overweight. It just means that every student should be required to carry at least one unit of PE every semester until graduation.
It's the parents fault for not demanding more of their children, and allowing their children to be lazy. Parents are to blame when they allow TV sets and game consoles in the child's room and leaving the toys in the garage. Parents are to blame when they give the child free money and allow that child to spend it freely on junk.
Parents and schools need to work together to ensure that the next generation of students are not allowed to become sedentary. Demand more of a child and the child will rise to those expectations.