You can do whatever you want with these dice. Most commonly, people will make up stories. Starting with "Once Upon A Time..." you roll the dice and continue the story. My 4 year old daughter plays with them, and my gaming group (ages 18-50) plays with them. They sell for around $7-9 US, and can be found in Walmart, game stores, and even in our Wegmans grocery stores. You can also buy them online at http://www.storycubes.com.
The older versions come in a little box that seals magnetically, and the newer version (seen above) has bigger dice and comes with a cool carrying bag. I have two copies already (one for home and I keep the other in my car for emergencies), but I'll be buying one of the new versions for my daughter's stocking, so she can have her own. She will usually roll the dice, tell a story, and then start over. The second time around she will change all of her rolls so they match the first rolls and then tell the same story all over again.
Click through the jump for the quick rules for our Story Cubes variant called Directors Cut.
