On a tray, place a pile of baking soda. Mix vinegar + a few drops of food coloring in a cup. Give the kids an eyedropper. Have them fill it with vinegar, squeeze onto the baking soda and watch mini volcanoes erupt!
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!!