Make colored sand art by stirring a chalk stick in a bowl of salt. it changes the color. Stir less for light color and more for dark richer color. (I used to do this with salt and food coloring. but the chalk stick idea is brilliant!
Use chemistry to make a bouncing polymer ball, then alter the procedure to see the effect the changes have on the characteristics of the bouncing ball.: Make a Bouncing Polymer Ball - Introduction and Materials
Rainbow Rice Garden for Play: Measure rice cups) and put it in a Ziploc bag with about of food coloring or liquid water colors (works great!) and 3 T of rubbing alcohol. mix the rice in the bags to spread the color.