I have my own pastels that I play with, but "adult" pastels have certain health hazards, so this is one art supply I didn't want to share with the kids. I bought them their own, nontoxic, Crayola oil pastels. Instant hit!
Oil pastels look like crayons to the kids, so their first impulse was to use them like crayons. But they glide on nice and slippery, and have a nicely saturated color, so there's novelty as well.