Put your pumpkins (or containers) in a bin or somewhere that would make the cleanup easier.
Mix the dry yeast and warm water together to activate the yeast. You could do this in the pumpkin but be careful you didn't cut a hole to low that it comes out before you're ready.
In another container mix the hydrogen peroxide, liquid dishwashing soap, and food dye together and mix.
Pour the hydrogen peroxide mixture over the yeast and watch it erupt.
We then repeated this experiment on the remaining pumpkins with different colors.
Since the resulting foam is composed of water, soap, and oxygen we went on to play with it. This is a perfect opportunity to swirl around the different colored foam if you made it multiple times.