This is a great idea for a project that allows preschoolers (or even older kids) to experiment with the process of creation, the most developmentally appropriate kind of art project,  and it also creates a product that you can send home for those parents that like something to put on the refrigerator to look pretty.

This No Time for Flashcards post details the process of creating art from a salad spinner!  You can make it fall related by having your cardstock paper cut into leaf shapes (IFLS librarians:  remember to avail yourself of the die cut machine capabilities, housed at Phillips Public Library!).  Use liquid tempra paint in a variety of colors (hopefully ones that will blend well together).  Have kids squirt it on the paper in whatever pattern they want.  Then they can spin the salad spinner for a few seconds, and take out the beautiful leaves.  For a better description (with photos), see the post.