Yes, you read that right, you don't even need to actually code the game, just write a general idea of one for the Children's Machine XO. Here's the official judging criteria that Samuel Klein, OLPC Director of Content, will use to score submissions:
Each entrant must supply a 100 word description of their game design idea which may be accompanied by an optional sketch or screenshot.As you start to put pencil, pen, or stylus to work on how to bring new life for old games on the Children's Machine XO, do check the contest fine print: only registered conference attendees qualify to enter, and you must be present to win.
The judges will be looking for game design ideas with particular attention given to games that make use of the laptop's special features -- its wireless mesh, human power, sunlight-readable display, and ebook or rotated-screen modes.
But don't let that stop your creative mind from exploring what could be. While I can't offer an OLPC as a prize, you can always add your new game ideas in the comments section below. Any submissions will be governed by the same CC-BY license as the contest. Your game ideas can be remixed and modified by others, with attribution to you.