Why just for kids? These camper beds would be fun for anyone.
While helping judge TreeHugger founder Graham Hill's LifeEdited competition, one of my favorite entries was the one by Borghese that put an airstream trailer in his apartment, shown below. It had everything you needed in a tiny space, and left the rest of the apartment open for other uses. Graham was not impressed but I still think about it, still like the idea.
That's why I also like these two beds designed by Mathy By Bols and shown on Contemporist. Imagine if this really was designed like a trailer, with solid soundproof walls. It might have a tiny air conditioner for hot nights. It could provide real separation and privacy if one is sharing the space. It's a lot roomier and more comfortable looking than Steven Johnson's Hiding capsule.
Why should kids have all the fun? This would make a lot of sense in a loft. Set it up like this: