Part of the trick with managing littles in an art class is to over plan your crafts. I try to always have several small "filler " projects ready. Some kids will get done quickly, and they can learn to do more work on their craft or learn to wait a little, but sometimes EVERYONE gets done quickly, and that is when the filler project can save your day.
This darling paper plate whale was a great time filler. I found the pattern at Krokotak.com. I pre-cut and folded them, the kids colored them and we helped glue on eyes at the end .