E-How has a simple tutorial on how to do this with your kids. You only need eggs, string or twine, a cloth or foil, a pot and water. Try it. It's easy.

Anna Anthropy’s great Twine tutorial walks through the entire process. Once complete, a Twine story can be exported as cross-platform friendly HTML using one of a few set templates.

Grab both ends of the string—preferably use pieces of wood or a couple of pens to wrap both ends, so that your hands get a better grip. Make sure the twine is taut.