Ok, you are going to crack up at this one... Mark LOVES trampolines. We don't have one simply because of the cost but some of our relatives do for their young children and when Mark can't be found in the kitchen eating, he's out there on that darn trampoline <img src="i/expressions/face-icon-small-smile.gif" border="0">
He thinks it's the greatest thing, much more fun that manual chest PT or the vest, and works well to help clear things out and get stuff moving.
I think if you got one (which I'm in favor of for CFers, any cardio is good for them!!!) you could use it as a treat sometimes to encourage them to use it. "if you do X, then you can go jump on the trampoline for 30 minutes" or something like that. But if they show a huge interest in it right away and that interest doesn't fade, then you probably don't need to use that kind of incentive.
Oh, Mark puts his vote in for a trampoline (he's such a kid sometimes, 25 going on 6) <img src="i/expressions/face-icon-small-smile.gif" border="0">