My fabulous friend and colleague Sue Abrahamson from the Waupaca Public Library shared a tidbit with me the other day about an experiment she was doing with kids about how many drops of water fit on a penny.
This is something that could work as an all-day, drop-in activity, where kids report their findings on a big chart:
or you could include it as an activity with other water-related or surface-tension experiments. Sounds like fun!