It's not clear to me that you should try to teach him. He understands the rules of the game and the goal, right? So play games with him. If you have supportive friends at your club or online, have them play with him. You might want to dispense a time-tested proverb once in a while, like "the first line is the line of death." Soon he'll be as good a a regular beginner and you can just make him an account on KGS.

As time goes on, if he gets to be the kind who likes to do puzzles on car trips, you can teach him how to do tsumego; if he turns into a bookworm, you can go through some go books together; if he starts getting really good, you can pay for lessons.

Think of learning Go as like learning a language. You aren't going to develop a lesson plan to teach your child English (if that's your native language); he's going to be fluent just by virtue of growing up casually practicing the language a great deal. As a child he will, of course, speak it in a childish way, and as a young adult he'll get a bit of specific instruction in how to speak, read, and write from professional language teachers, but trying to drill him in grammar and giving him vocabulary lists, the way you would with an adult who was learning English for the first time, would be counter-productive.

Doing tsumego as a standalone puzzles will be best way to start, then atari-go.

I worry about atari-go and his age because I don't want him to think it's a game about capturing primarily. He's young enough that if he gets that idea into his head that it might be quite hard to break the habit of constantly trying to capture opposing stones.

That's a phase he is likely to go through anyhow.

Ah okay, well we're in agreement there. Here I think you can't go wrong with vocabulary and proverbs. I don't think that the guy who ran my preschool was that good at chess either, but he dropped things like "a rook on an open file is liquid gold" which have stuck with me my whole life.

If he's having trouble grasping the point of the game, you might go with stone scoring and tell him the point of the game is to get more stones on the board than the opponent. That will help him understand both territory and why you want to capture pretty quickly.

Arbitrarily disallowing the 3-3seems silly... Why not just make it 13 stones? Or 17?

Thanks for the links and ideas. One of my 5 yr old twin girls is very interested in Go. I've had her doing the opening set of of problem on GoChild. She loves the it and has a good grasp of liberties and groups now.

Working up to playing with my board and stones but she gets a little wild sometimes and the stones get scattered

Who knows, if we ever get an KGS app for it, she'd play whenever she could on her Kindle Fire.

I worry about atari-go and his age because I don't want him to think it's a game about capturing primarily. He's young enough that if he gets that idea into his head that it might be quite hard to break the habit of constantly trying to capture opposing stones.

If you put on a different rom, it will run KGS.