Hi again Show!
I hope your son has fun. Is this his first trip to Europe? I'm not a seasoned European traveler, but on my one and only trip, I travelled alone, but met friends there. I guess that's a bit similar. This was about 15+ years ago, so maybe things have changed. But here's what I recall by way of "tips."
Change money at a Currency Exchange - NOT the hotel. While most hotels will change currencies, their rates are much higher.
Don't let anyone, especially kids, "offer" to take your son (or girlfriend's) camera and snap a pic of them together. I know a few folks who ended up with stolen cameras over that one.
Enjoy Paris!!! Even if as an American, he is not made to feel especially welcome by the population at large. See the historic sites, enjoy the food, and find other *internationals* who willingly help with directions. (Sorry - I don't mean to offend anyone from Paris on this board - I just didn't find it to be the most friendly place as a tourist!)
I'm sure this will be an awesome experience for your son!!!
DG