According to Kids' Science Experiments, all you need for this experiment is a standard two-liter bottle of cola and a roll of Mentos mints. Take the lid off the soda bottle and drop five or six of the Mentos in. Within seconds, you'll have converted a beverage into a shooting rocket, because of the chemical interaction between the cola and the Mentos. You'll want to do this somewhere that's very easy to clean -- or just ourdoors.
Take some old pennies that have darkened with tarnish and soil and put them on a plate. Then, cover them with barbecue sauce. After a few minutes, dump the pennies into a bowl and rinse them off with tap water. They're bright and shiny again, because of the interaction between the acids in the barbecue sauce and the metal.
Watching things dissolve can be fascinating for young scientists. According to the American Chemical Society, if you add sugar cubes to three different cups, and then add substances like water, olive oil and rubbing alcohol to the three cups, you'll notice that the water dissolves the sugar much more quickly than the other two liquids. Water's molecular properties make it a better solvent for sugar.
Which will bubble up more in hydrogen peroxide? According to TLC Family, it's fairly easy to test this. Once you have your kids chop up a potato and some raw liver into small pieces of equal size, they can add some hydrogen peroxide to some test tubes. Add a drop of dish soap to each tube and then add a piece of liver to one and potato to the other. Measure the height of the foam in each one. Liver should win, because it has more catalase, which breaks down hydrogen peroxide into water, releasing oxygen.