http://www.reddit.com/r/gamedev/comments/11i1z7/game_development_for_children/
I just added a FAQ sectiona FAQ section for the best answer I could come up with, since we often get this question: "okay so if I can't ask it here, then where should I ask it?"
In my opinion, though, this question falls under the last bullet point; it seems you've already done some research, so I'd suggest you simply pick one of the tools you think would be good and sit your child in front of it, and see if he likes it. Or try them yourself to see what you think. Everyone will have their own experiences and opinions about the different tools but you're unlikely to get a solid answer, other than your fears about isolation are unfounded and any experience is good experience.
And that, by the way, is why this is not a good fit for our site. :-P