I hate prebuilt kits, but I think the one for kids tha Major's has seems about right for k-8? I think (HOPE!) most high school students can be trusted with a little more, but not much. Schools are poor.

http://www.majorsurplusnsurvival.com/Mer...Category_Code=9

I'd add a poncho, and a dust mask, but that would be it for something that is going to mass stored for students. Distribution is the only glitch I can think of.