I wasn't really taught that excess caloric intake = increased body fat when I was a kid and I guess no kid really should. Parents need to be taught so that they can be that health-buffer.
By way of contrast, my parents restricted me to 600 calories a day when I was 7 and spent 8 months requiring me to do half an hour of Canadian Air Force calisthenics before bed. And when that didn't work, they gave up.
When I went from outweighing my father by 50 lbs to underweighing my father by 50lbs in the space of three months, they said "congratulations."
I'm 7 inches taller than my father.