While It’s Cold, Teach Your Kids To Snap Freeze Water Bottles
Snap freezing a water bottle is an incredibly cool little tidbit of science. It's really easy to do, and a bottle of water is the perfect cheap vessel to try this with.
I wouldn't recommend you leaving a bottle of water in the seat of your car... I know from experience... But you can do this in the freezer, or out on the porch if you protect your bottles from the wind. Also, try this with a few bottles in case one doesn't work.
Here's how it works.