If you've ever been to a paintball fight, you know that the guns are heavy, the paint is really messy and doesn't smell very good, and that the paintballs hurt when they hit you. And if you've ever wanted to bring your kids to play, you know that most places have a minimum age of 11 or 12, for all of those reasons (plus liability insurance, no doubt).
Now there's a safer, lighter, much less-messy version of paintball — only it doesn't use paint in any form. It's called WipeOut, and it comes as set of two guns, each of which holds and can shoot foam-tipped darts that leave a smear of chalk dust when they hit. The kit also comes with two pairs of safety glasses, because of course chalk dust in the eye would not be much fun. The guns are spring-loaded, so their range is considerably more limited than paintball guns, but as a parent I'm not sure that's a bad thing.
Chalk dust cleans up easily, and the darts seem to be essentially Nerf-plus-chalk, so there's little to object to about them. They've been safety-tested for children age eight and up, though most kids six and up would be able to handle the guns without much difficulty. They're very obviously toys by their appearance, so I look at them the same way I do water guns: not quite gun-like enough to make me nervous about letting my kids play with them.
The two-gun kit retails for $40, and a six-dart refill pack retails for $11.