Almost everybody with a garden has slightly over-ripe cucumbers. They are the best ones to use and this way they aren't a total waste. You'll need to get just a few things together before you start.
For each boat you'll need:
One popsicle stick
One piece of stiff paper colored for the boat's flag
One large paper clip
One large over-ripe cucumber
An adult will need to cut each cucumber. Cut it lengthwise so that about 2/3 of the cucumber is left. Then the adult is free to take the knife and leave if they want to.
While the cukes are being cut, the kids can fasten the flag paper to the popsicle stick with the large paper clip.
Take a spoon and scoop all of the seeds out of the cucumber.
Stick the bottom of the popsicle flag into the fleshy part of the cucumber. Be careful not to go all the way through the skin or you'll spring a leak.
Your cucumber boat will float on a creek or pond while the kids wade beside them. If flowing water isn't available, a wading pool or even a washtub full of cool water will work fine.
The beauty of this project is that when the kids are done, the boats and leavings from building them can go to feed the animals or even into the compost pile.
So the kids are cool and happy on a hot summer day and all it costs is the time to cut up a cucumber. Bon voyage!