a good project to do, but can be costly if you are using film, is to do "a day in the life of" where they take photo's of themselves or what they did during the day. It can be simply things like a picture of an alarm clock, or a bowl of cereal in the morning, but the idea is to have the kids share a typical day for them through a handful of pictures.
another good project would be to take your name, and for every letter of your name take a picture of something that starts with that letter. For example, my name is Kyle, so I could take a picture of a Keychain, a yo-yo (Y is hard), a lightbulb, and an earing (just to name a few common items). Try to encourage more than snapshots.
really any kind of story telling or other project that requires a series of pictures is fairly easy to do. If you are trying to get these kids to learn better composition and exposure type issues, then you'll probably want something a little more sophisticated, something like "how many different ways can you photogragh _______" and they can take pictures from different perspectives of the same subject. A great example of this would be any form of moving water (for shutter speeds), or for composition, a tree. They can take a picture of a tree from far back, or they can get underneath the tree, hold the camera at the base of the tree and shoot up the trunk, stand a little ways away and take a picture from a "bugs perspective"... crazy things like that.