Bring a stack of copier paper and let the kids make lots and lots of paper airplanes. Then you need some way to clearly divide the room in half. (The taller the divider the better.) A couch works, but even better was a rolling chalk board. Put half the kids on each side of the divider. Put half the paper airplanes on each side of the divider. Explain that they can only throw ONE plane at a time and they must stop when the leader says "stop". Say "Go". They throw the airplanes over the divider as fast as they can. Planes are flying in both directions. Let them go about 3 minutes. Give them a ten second warning and then say "stop". Count the airplanes on each side of the divider. The team with the least number of planes wins. Repeat it a number of times, keeping track of the wins to get the champions.
A quicker variation: Throw a big bag of loose socks.