Have the birthday child blow through a funnel to put them out, while you talk about air pressure. Exploding' capsules that expand into sponge animals or things, tablets for bath that turn colors or fizz. Ask some teens or pre-teens to be the lab team leaders and take a group. Have each team paint a volcano landscape previously made out of papier-m ch formed around a 2 liter soda bottle. They can also set up a town scene around the volcano using mini people, legos, etc.
Colors range from blue to yellow to pink to orange.
You boil about a cup of shredded red cabbage until the water is dark, strain it, and then dilute with water until it's medium purple rather than black. You don't want to mix ammonia with bleach, for instance. It's heavier than the alcohol but lighter than the water, and if it gets equal pressure from all sides, it makes a cool sphere. Add green food coloring to look like ooze. Gravity or you can pull on the molecules.