I kinda agree. I'm a fat woman and have a fat husband but we have managed to keep our kids at a healthy size. I frequently see skinny adults with fat kids and think "what the f**k?"
But there are problems with legislating it. Except in cases of morbid obesity, it can be difficult to determine if a child is obese. A child is developing, and may put on weight before a growth spurt. Children also develop in different ways. Another problem is that if you intervene in a way that causes a child to develop body image issues, you may create new problems which can be just as bad.
I do get where you're coming from. I see atrocious behaviour from parents all the time. Such as...
...using food to pacify a child in a situation where letting them play out the energy would be totally appropriate.
...preventing the child from making healthy decisions (I worked at a restaurant where the standard side item was carrot sticks. When they ordered we would tell them that. Most of the time, the child would say "that's fine" and the parent would say "they won't eat that, give them french fries." I also worked at a snack cart where fresh fruit was an option. Kids would often actually ask for fruit and parents would often say that they needed "real" food, and go get a burger and fries.)
...Saying no, but then giving in forgetting that they are the parent. (Same snack stand, a kid asks for a bag of Cheetos. It is no later than 11am. I hear the mom say "No, you've already had three bags today." I suggest fruit "how about a piece of pineapple?" The mom says to me, with an attitude, "If he would eat that sort of stuff I would be over the moon." She ended up getting him the Cheetos.)
...Letting older kids avoid basic exercise. (School age children, absent disabilities, should walk. They don't belong in strollers.)