The best online resource I've found is the beginner and intermediate lessons (with video) by Justin Sandercoe: www.justinguitar.com
All of the lessons are free. For whatever reason, his delivery style works with me, and I've progressed faster from his lessons than from anywhere else. Plus, if you can get your hands on his beginner songbook for your son, that thing is great. 100 or so songs, with easy to follow along chords and tabs. He has a ton of resources on his site, with the intermediate stuff being too advanced for me. I'm still working on the beginner lessons.
Unlike other online lessons, I don't get bored with his. He does have some videos of chord walk throughs for a decent amount of songs. This stuff may be too easy for him...for me it's been really helpful.