One of the most effective ways to keep kids occupied for the last, oh, 40 years or thereabouts has been to give them a tub or two of Play-Doh and maybe the garlic press and let them go to town. It kept you busy and out of your parents' hair when you were little and so it will for your children, too. You recognize that distinctive Play-Doh smell, don't you? Open a tub and take a whiff—nostalgia in a plastic container is what that is.
Play-Doh is, like many things beloved by small children, not without its drawbacks. Most of all, it gets everywhere. Small balls of Play-Doh scattered as far as the eye can see, and of course squished into the rug. Play-Doh of course tells you that it's easy to clean up: simply let it dry and vacuum it out of the carpet.