JBL, After reading your last post, it would seem that you are way more qualified to answer your question than most buzzards. While I'm guessing most people would not take a child as young as your's on the river, you seem to have taken a lot of time and effort to advance your river skills and also to help prepare your son and outfit him properly. Without the background info that you have now given, I didn't feel like I could offer an opinion other than what I said.
So, as I said before, go with your gut. You obviously understand the risks and the consequences, which can't be said with a lot of people.
When our kids where very young, we use to take then sailing on Hobie Cats, which if you don't know, are very tippy boats if the wind comes up. I use to race Hobie's and was comfortable with my skill to keep my kids safe.
As a parent, the one thing I've always found interesting is the amount of knowledgeable information you can get from people that don't have kids.
As I like to joke with new parents, just read the manual that they gave you at the hospital. All the answers are there.
By the way, mind if I join you on that R/H, WW trip. Sounds fun!