All you need for this fun project are some colored markers and some clear acetate. The markers can be either water-based or permanent. Cut the acetate into small rectangles (1.5" x 2") , and give two or three of them to each child.
Have the kids make mini-designs of their choice on each rectangle. Tell them that the more lines and shapes they fill in, the better!
Then mount the mini-creations in slide mounts, and either import them into a computer with a slide scanner or put on an actual slideshow the old-fashioned way, with a real projector. Popcorn and music would go nicely with your presentation.