I love engaging my childrens’ creative inventing juices. It is wonderful to set up a project and then step back (usually with my camera in hand) to watch the fun. Nearly always my kids don’t actually end up with an unadulterated version of the intended project, but they have a ton of fun and add their own creative mark.
Here is one to try with your kids: the Archimedes Screw. All it takes is a few simple “ingredients” you can easily find in your home.
Maybe you can even take your kids outside and build a larger version in the sandbox, turn on the water hose, and see if you can ‘lift’ water as the ancients did.
Have fun!