I gave Aidan a Pocket Vocano that has a chamber for baking soda; one pours vinegar into it--instant lava. It was fun, but at about 2", produced a rather wussy explosion. So I conceived the brilliant idea of building a bigger one in the sandbox. We used a toilet paper tube for the volcanic chimney, packing it with baking soda. Then--so the "lava" would have some hint of fire, I added red food coloring to the vinegar, producing "volcano juice." John played volcano god. As you can see, the result was a delight to the six year old's heart. His three year old brother was pretty impressed, too. Alas, we only had enough volcano juice for three eruptions, but I promised him next time he comes, I'll have a full bottle, and we'll build a whole range of volcanoes & set them off at once.