Who would give their child a whole baked potato? Isn't that an adult portion?
In the 50s and 60s, children were fed half portions until they were the same size as adults, whenever that happened. Children's plates were used, or a tea plate - which was much smaller than a dinner plate.
No snacks at all, except for school milk (no biscuits) and in our case, a cup of cocoa mid-morning as under-5s at home.
No-one used a mug. Cups only, so even drinks were smaller. Toast was a breakfast treat, with the boiled egg.
On Friday, we were given a bar of chocolate - the smallest size (ie tiny). And our Friday evening routine in summer was a walk, with the chocolate handed out half way around. The walk took two hours. We did a similar walk on Sundays and we played outdoors constantly unless there was torrential rain. This changed a bit as we approached our teens but we were used to exercise I suppose, and by then we would be cycling on our own, or playing tennis and so on. You didn't hang around indoors or an adult would "find you something to do", which meant extra chores!
There's no mystery to the so-called obesity epidemic. We eat more than we need, we serve children adult portions, and we eat the wrong stuff. All this "kids need carbs" would be fine, if the kids involved were also eating protein and running around constantly. If they're spending hours on the sofa, watching screens, they need very little.
I am amazed when adults say their children get plenty of exercise and then cite an hour's swimming, a gentle bike ride, an hour's gymnastics or whatever...once a week! That is nothing.