I have raised 5 kids and I may be wrong about this but I think it is because kids are bored and don't get enough exercise at home and at school. Kids at one time when they got home from school they would go outside and play now all they do is sit on the sofa and watch TV or play video games. At school kids would go play in the yards now all they do is sit on benches and do nothing. They don't even use their minds, they do nothing creative at home or school. They build nothing, everything is on computers or calculators. When is the last time you saw a kid cutting grass or building something in the yard? They hate to get out of the AC because its to hot outside or to cold outside.
Most are overweight and eat junk food instead of healthy food.
Don't blame the kids as it is the parents fault.
This doesn't apply to all but most.