Now this is something I've got to try. With only minimal materials you probably have lying around the house, make an outdoor activity that will (depending on the temperature) potentially yield hours of fun.
Caz from A Little Learning for Two came up with this simple but ingenious activity involving balloons, toys, and ice. Just put something tiny and interesting into a water balloon, freeze overnight, and voila! You have day's journey ahead of you. Make it a game by hiding them, add to the science aspect by providing magnifying glasses. Just the thing for a warm weekend ahead.
Learn more: A Little Learning for Two
(Images: Caz at A Little Learning for Two)