Considering how health crazy America is at the moment, this seems VERY counter-productive to solving the obesity problem. By doing this, you're only going to make children stay inside and get fatter.
I played those kinds of games all the time when I was younger, and the only kind of injuries I suffer were scrapped knees, some cuts, and maybe a little loss of pride through losing. But that's all part of growing up. Not only are these games fun, but they toughen you up and teach you humility and good sportsmanship.
By taking away these things, you're only hurting your children in the long run and making them into crappy adults. And that can cause harm to not only them, but in a way America as well. Because these children will eventually be the ones running the country.
Maybe I'm being a little harsh, but that's how I feel about this kind of thing.