Some friends of mine have found a good way to get their children away from playing games on their computer and watching too much television.
They have installed a trampoline in the garden. It is surrounded by a net so that they cannot fall and hurt themselves.
I'm on my second trampoline, the first one went over next door's fence when we had a gale. The kids are always on it, even in the rain, it's the best money I've ever spent.