Next I asked the girls if they think the balloon could fill up with air all by itself.. I explained that when air gets hot, the particles move around very fast and bump into each other (we ran around the room and demonstrated), and when they get cold they stand still and shiver (we demonstrated that too). I put the balloon around the opening of an empty soda bottle and boiled some water in the microwave. The girls observed the bubbles that we coming up from the boiling water. We then plunged the bottle into the hot water to see what would happen:
For our next experiment, I asked the girls what would happen to paper if we put it in water (it would get wet), and then told them that I knew a trick for keeping paper dry in water. First, L crumpled up a piece of paper and stuffed it into a cup. Then I showed her how to plunge the cup straight down into the water without tipping it (she then did it herself).
We probably didn't need to do so many experiments to demonstrate the properties of air, but it was so much fun that we just kept going and going all afternoon, and the kids even continued the experimentation as they took a bath!
I know that these experiments made an impression on them because a couple days later, E asked me if I remembered when we inflated the balloon by putting it in hot water, and proceeded to describe the experiments and results to me, completely on her own.