Have you used bleeding tissue paper before? This idea at Crayon Wishes and Popsicle Dreams was an activity at a Rainbow Art birthday party. The result makes beautiful stand-alone art but could also be used as a layer in multi-media art.
Are you intrigued by the idea of making your own bouncy balls? About.com shows you how to make them with borax, corn starch, and white glue. What a fun way to introduce chemistry to kids!