Our next door neighbor erected a trampoline in their backyard last summer. It was pretty popular. For two days. Another yard in the neighborhood has one. I've never seen anybody actually use it, but their big black dog loves to lounge on it. Not sure what the 'interest' lifespan of a trampoline is, but if your family's enthusiasm is on the down-slide, it might be time to turn it into a suspended bed. (If you don't have one, I'm guessing Craigslist has plenty from which to choose.) Atlantic Trampolines in the UK gives us some suggestions on how to do such a thing. Click here for more info and examples.
How to recycle your Garden Trampoline [Atlantic Trampolines]