Heroes and Danger: A Role-Playing Game for Pre-Literate Children

From the introduction:

In the summer of last year I babysat once a week for a family of three kids: four, six, and eight years old. Being an adult nerd I see it as my personal responsibility to bring up the next generation, so I looked around for a tabletop role-playing game suitable for children. As far as I could tell, the kids' games on the market were geared toward a slightly older age group—kids with a firm grasp on reading and basic math. So, I set out to design a game suitable for kids as young as four.

Originally I'd hoped to come up with something I could publish for profit, but in each iteration I removed more and more from the rules until now they would fit comfortably on an index card...I call my system Heroes and Danger.