Imagination Starters Chalkboard Crayons. These are have a unique formula that is non-toxic, washable and wipes off with just water. These work great on their placemats and flash cards and even glass! They also work on non-porous chalkboard but since no one ever knows if their board is, use caution and test in a corner to be safe.
Colors included: Red, Orange, Yellow, Green, Blue, Purple, White, and Brown