Armed... I'd want some sort of homemade super soaker type weapon, made out of a light, but strong metal. Full of acid. The strongest acid that wouldn't eat through the weapon itself. A backpack for extra acid would be nice as well.
First I would spray the floor in a circle around me. If the children are wearing sneakers, the acid would burn through their shoes lickety-split and they would fall, burning their little hands and knees. Assuming I put enough of an acid perimeter around myself, this would give me time to pump up the weapon or reload while kicking the screaming injured wee ones back into the puddle.
As the hordes kept coming I'd have to keep spraying the floor and kicking or clubbing them back. I figure I could kill or horribly disfigure/immobilize around 50 to 60 kids this way, but at that point they could potentially climb over the bodies of their fallen comrades without getting a drop of acid on them. My "circle of safety" would surely be smaller as well, so I'd have to start spraying them in the face as soon as they're in my line of sight. I'd inevitably run out of acid, at which point I would club as many of them in the face as possible.
As a last resort I would climb out of the pit of bodies and run like hell, hopefully managing to survive another five minutes with only my empty acid gun, using it as a club.
Before I succumb to the onslaught, I figure I could take out well over a hundred of them. Maybe a few more if I back into a corner.
Unarmed, however... Shit. Not many, maybe 10-15 tops. 5 year olds are tough, especially trained and in great numbers.
Oh, and Spike, thanks for raising this particular dead thread. Some great laughs to be had here. Much like Crow, I have no idea how I missed this in it's first run. I must have been sleeping.