You are talking about "SOFT AIR" guns, right? These are not to be confused with the high power air guns that is the new fad for hunting now days.

Soft Air guns are very weak air guns that fire those blasted little yellow bb's you see in sporting good stores. Most bows shoot faster than these do. In my opinion, they are very dangerous for kids. It's easy to get into a "combat" scenerio with friends and there goes the eyes if not protected. Plus, they bounce back at ya if you hit something solid.
Most are single pump type pistols, rifles, and shotgun type actions, but you can get battery powered full auto versions. They run anywhere from 10.95 to 29.95 depending on what you get. The pump riot shotgun is kind of cool though. They will leave marks on the body if you're hit with them inside 10 yards or so.

Basically, they are toys.