Snails are so easy to find and very interesting for little ones.
Just get a snai or too and add some water and some bread to a plate. Place it on it and wait until they get out to eat. Might help to bring them close to the bread to sense the smell. They might soil your plate, but that in itself seems to be funny for kids. Do put the snail back in nature, maybe give it a name and say bye, bye.