My kids love doing this. You will need:
*a cookie sheet with sides (to catch the excess liquid and foam from the volcanoes)
*food coloring (if you want to color the volcanoes)
*canning jars or glasses
Place glasses or canning jars on cookie sheet. Add about 1/3 cup of vinegar to each glass. Add a drop of food coloring to each glass. Then let your child spoon in the baking soda. You can add more vinegar and baking soda after each volcano settles down to make it active again.