You start out unarmed, but you gotta figure that if you're in a big empty warehouse, there's bound to be a 2x4 or a metal pipe (or if you're exceptionally lucky, a crowbar) laying around somewhere. Figuring that the average 3rd-grader is going to weigh around 60lbs or so, using one of them as a weapon isn't really a good idea... too heavy to swing more than once without losing your balance, no sharp edges to take heads off with, and it's highly unlikely that you'd be able to simply rip a limb off and use that. Human tissue is remarkably tough and difficult to tear. Heck, even chicken skin takes quite a bit of effort to tear bare-handed. If they're "rage-zombies", your best bet would be to run, find some high ground where you could kick them down as they try to climb up for you. A three-story drop is usually enough to cause a significant amount of bone breakage in an adult to render the person either immobile or at least severely compromised, but little kids tend to be very flexable and have soft bones that don't break easily, so you're looking at an extended fight. The best bet would be to find some cover, hopefully in a defensible location within the warehouse, then find something that can be used as an improvised weapon. I figure that most people could take out two, maybe three of the little buggers before the swarm overtakes them. Remember, while you're twisting one of their little heads off with your bare hands or bashing it in with your scavenged bit of catwalk railing, the other hundred are going to be climbing up your legs, biting chunks out of your ankles, and getting their jelly-and-blood smeared fingers into your eyes & mouth.
Great, now I'm gonna have nightmares tonight about this senario.
**All this plan is missing is a giantfreaking laser in space."**