How about an i-spy sort of crazy quilt. Let the kids color/design the central area and then you incorporate it into the quilt via crazy patching.
Or the kids can cut out appliques to put on a quilt. That way if you have the background quilt already mostly done all you do is fuse and ? sew on the appliques.
Most kids would like to see a jelly roll race, esp if you have 2 people and 2 machines. Heck, even adults will stop for that. If you want you could add applique to those quilts.