My oldest son is just starting to use the computer to play his 'letter game' as he calls it. I can see this coming in handy soon. Just out of curiosity how do you kick this off and do you have it set up in such a way to prevent him from disabling it? I suppose it could turn into an arms race but he would certainly learn something in the process. It's not like an off the shelf solution that would have hacks posted for it all over the net.

BTW, starfall is a nice educational site for young children.