It isn't just the children that are obese though, often it is the entire family. Look at what is in food these days, I don't mean sugar, I mean the fats and additives, lack of exercise, sitting around with screens, watching TV, driving everywhere.
Very few children were overweight at all, some were a bit more sturdy but none seriously or noticeably overweight when I was at school, both parents worked but ready meals and burgers were hardly ever seen and were a treat rather than part of life.
I was sent out to play, walked to the bus stop for school, or often had to walk to school if the bus was full, activities involved moving about, not sitting indoors with a screen. My mother cooked when she got home from work, it was plain cooking, didn't take all evening. My parents weren't fat. The pace of life was slower and we weren't bombarded with burgers and fried chicken, there was one phone in the house, no screens to be attached to.
These days people don't want to move about, they drive everywhere, buy ready meals and junk food.