I would definitely consider it as an option but the only real judo school over here is pretty steep. They charge over $70 per month if I'm not mistaken and they mainly only teach adults. It's a really good school from what I hear, but money talks.
Fuck paying $70 a month, I think your kid is just as well off with a school that focusses more on the sport aspect of judo on that age.
He'll learn a lot either way at that age. And don't forget he also should have fun doing so. Or else it would be pretty pointless because he won't keep it up anyway.
Also I forgot to add that Judo is probably the cheapest yet effective martial art.
I've seen some dojos that are $50 a month, here in the expensive Bay Area. Other places much cheaper... history has it back in Japan, Karate was for the rich and Judo for the people who couldn't afford Karate.
I am so fortunate to live in a country where there is so much and such a high standard for matial arts. Keeps the prices low. Except for krav maga but if I want to learn how to run away from a fight I'd pick up running. Probably stepped on some toes there!
That history about rich and poor got pretty much shot down when most martial arts made it to the west.
I pay about 20 euro's each month but I also get private lessons from my teacher at least twice a week for what I pay absolutely nothing. He is one of the few that still maintains this mentality of not accepting money to teach this art.
Personally I am not such a big fan of Muay Thai or Thai boxing, it's a beautiful art and yes you can kick someones ass probably (if you are trained better then your opponent) but it relays heavily on speed and strength, both of which diminish when you get older so you are more likely to lose a fight of a younger but stronger and faster while less experienced guy the longer you train. While in fact the longer you train the better you should become.
At this moment I train a lot of mechanics for punching and hitting, it's all technique, a decent punch has actually nothing to do with strength. You should also not even be in a fight, ever. When someone comes at you with aggression hit first and hard knocking him out with one punch but throw three just to make sure and talk after. My teacher always tells me if you can't knock someone out in one punch you just can't punch lol