Make a worm farm with the children. You can either buy your worms at a bait store or if possible have the children help dig for them. Use a small fish tank or terrarium container. Fill it with soil. Place the worms on top of the soil. Place black or dark colored paper around the tank to block out the light. Place some lettuce, grass cuttings, or wet old leaves on top of the soil. This will be food for the worms. After 2 days, remove the paper and children will be able to see the tracks the worms have made moving around their new home.
Recently I rescued some real live earth worms and included them into my sand and water table along with some dirt and a spray bottle full of water. The children loved feeling of them and measuring and comparing their size length, etc. After a couple of days we released them into our small outside garden which was a good example of recycling. Just as long as you keep the soil moist and a few tidbits of scraps in the sand and water table the worms will thrive. Good luck!