Glad to hear progress is still being made. But I second the suggestion to keep it small. Kids aren't exactly capable of long-term planning when they're little. Making a small game would be quite an accomplishment by itself and the pride in seeing what he accomplished might be enough to spur him on to bigger games when he's a little older. 
Good luck with the project. I hope you two make it across the finish line.

Good luck with the project. I hope you two make it across the finish line.