8 years old
Red food coloring
Countertop chemistry experiment that can be used for a potions class.
I found this experiment in an American Girl magazine. They called it Red-Hot Retro, and basically you're making a mini-lava lamp.
You'll need a tumbler, half filled with water. Add red food coloring, stir, and then add vegetable oil until the glass is almost full.
Then add some coarse/kosher salt to make the oil bubble. Add more salt to make it bubble again when it slows down.