I've gathered a bunch of Montessori ideas from the books I've ready and here is our latest experiment.
Gather a bunch of different items that won't be ruined by water, a dishpan (or bucket!) of water and a towel. Then ask, "Does it sink or float?"
Ha! Even the dog was interested. (In the water, that is.) Ladybug didn't quite catch on completely, but it introduced a new concept and we'll bring it out again later.