First, find two cans that, when empty, just fit inside each other. (Mom was nice enough to find some out-of-date ones in her pantry and empty and clean them out when she came. She's also very smart--she brought a set for each kid.) Then, punch a hole in the end of the can so a firecracker will fit very snugly.
Pour a small amount of water in the large can. (You'll learn that the amount of water affects the height the can goes--that's the fun part, experimenting)
Place the can with the firecracker in like this:
Mom says the secret is to put the can in the can with water, then put the firecracker in.
The can will launch into the air.
Collect the can, and do it all over again.
To see more photos and read more about our family celebrates the Fourth, go here.