Kid friendly Elephant Toothpaste shows the difference in reactions with various concentrations of hydrogen peroxide.
How to make "elephant's toothpaste" and teach your kids about catalysts at the same time
Fun Science for Kids: Elephant Toothpaste!
Fun Science Experiment for Kids: Elephant Toothpaste! from Fun at Home with Kids (could be a fun Harry Potter potion)
Classic Science at Home: Elephant Toothpaste
You will need: a clear plastic or glass bottle, a funnel, a dish or tray with a lip of at least 1 or 2 inches, 1 teaspoon of yeast, 1 big squirt of dish soap, 1/2 cup of hydrogen peroxide, food coloring
Lemon volcanoes, crystal rainbows, and color clouds -- these fun and easy DIY science experiments will wow the whole family.