I'm overweight, very much so. This is an ongoing issue that I'm dealing with.
My DS is ideal weight, despite having me as a terrible role model. He doesn't do a massive amount of exercise as far as I'm concerned, swimming, gymnastics, cycling and the usual running about. I see parents talking about lots of exercise but I think they are kidding myself. Most Saturdays my DP takes DS swimming and soft play, probably 40 mins each, then we all go on a dog walk which is usually 2 hours. DS is is quite happy to go for film night as his cousins afterwards. So I'd say he's fit but if I was less lazy there's definitely room for more exercise.
Hes always hungry and can help himself to food, but he has to eat meals. If he didn't fancy he's breakfast there's no snacks till lunch. And I rarely let him drink milk as this fills him up.
I don't think people are intentionally harming their children (obviously!) but it is what's happening.
I don't think the answers is letters giving you a telling off. In the same way that post war when children were found to be neutritionally starved rose hyp syrup and whole milk were distributed to all I think there needs to be a whole society approach.
Plenty of countries having daily exercise at school. Exercise that makes your sweat and pant not standing in lines waiting for a turn of hitting a ball.
I won't happen though. Too expensive and no immediate results. 50 years down the line though people will wish it had happened.