Hi ultramarina,
I remember seeing your posts over a year ago about your then 3-year old son's amazing chess ability. I don't have any specific software recommendations (DS11 has moved on to chess software for adults).
In terms of books though, I highly recommend "How to beat your dad at chess". It's available in most bookstores, and you should be able to read it and determine if it's a good fit for your son.
It might also be time for him to play at actual tournaments. For kids 8 and under, there are usually short games where an entire 4-game tournament is over within a couple of hours. And depending upon how he likes it, and his maturity level, coaching might be the next step.
I know this activity quite well. Let me know if you have additional questions, and feel free to send a PM.
