Well, if any computer game is good for young kids, it would probably be Minecraft. You can look at it as infinite Legos at a fraction of the cost. I'd imagine it's a good way to build spacial skills and planning. Maybe a good opportunity to build some things together and collaborate. As a kid, I spent many hours digging through the Lego bins, talking about whatever with a friend or just freebuilding by myself and creating worlds. I don't play Minecraft that much these days, but I still value having my own private little world where I can go to be free from the everyday. I think even a 6-year-old may value that aspect.
6 is pretty young though, and the point about online interactions is very valid, although I have not played multiplayer Minecraft myself.