You want more active kids in the US? This is easy. Every neighborhood needs to have multiple adjacent lots with no construction on it. Aka, a park of sorts. It doesn't need to have slides, or games, or any of that other stuff. It just needs to be an open space with enough room that groups of kids can go and engage in outdoor activities without the need to be constantly monitored by adults. That's it.
They can play football or baseball or soccer or frisbee or tag. Doesn't matter. What matters is that you give them the room and let them do their own thing. Not only would this help them be more active, but it'd help them socialize a great deal more than they normally do.