For a quick easy science project try this…Cut two sponges in the shape of a cactus. Get one wet and leave the other dry. Talk about how it seldom rains in the desert and the cactus has to store water to survive (just like the sponge).
Leave your sponges sit out on a tray and let the children observe what happens
over time. Keep one sponge dry so that the kids can use it as a comparison.