Make erupting ice chalk paint. 1/4 cup each baking soda and cornstarch. add liquid watercolor paint and 1/2 cup water. Mix well w/spoon. Pour into ice cub tray freeze. After it starts to melt, use squeeze bottle or baster to add vinegar make them foam.
Another Pinner said: This kept my 2 year busy for an entire hour and my 4 year old busy for 2 hours! YAY! Drop vinegar tinted with food coloring onto a pan filled with baking soda. Sheer minutes of colorful fizziness!!... Pretty sure we will be doing this soon! GENIUS!.