TBH, I'd let them.
Scrumping for apples is a classic kid thing to do, almost a rite of passage... and if all they're doing is that, rather than getting doped up, nicking cars, smoking fags, or generally being complete ***** like most of the kids round here, then I think you're doing them, their parents and the community a massive favour by keeping them on a sensible path.
If you're set on destroying their childhood, then I'd think just the cheapy project box for Pi would be fine. It'd teach you a lot about the workings behind it at the same time.