Grandma and Grandpa D. sent a Steve Spangler Soda Foundation kit. Basically, it drops Mentos into a two-liter bottle of soda when you pull the string. The result is a spraying fountain of soda that's pretty impressive!
Here's the video of what happened:
Pretty cool, huh?
And here's the science lesson: The teeny tiny pits (nucleation sites for you geeks out there) all over the surface of the Mentos collect the carbon dioxide bubbles in the soda. When the Mentos hit the soda the bubbles form all over the candy and rise quickly to the surface -- up and out of the bottle in an awesome blast.
This was such a hit that I'll have to go looking for more on the science of explosions. Surely some homeschooler out there has written that curriculum for the preschool set!