In my opinion it would depend on a few things. There would be no contact sparring of any kind. This was heavily supervised by trustworthy and responsible adults and not some young kid who doesnt care about the kids. And I'd probably want to be there to watch each time he goes.
I started boxing when I was 12 and it was insanely helpful to me. It gave me confidence and I made friends with a lot of guys. It also helped me be popular and get laid in high school. I was always in shape and could kick any bully's ass. I probably would have started in mma but it wasnt around when I was a kid.
I'd say go for it but be cautious.
If a law is unjust, a man is not only right to disobey it, he is obligated to do so. ~ Thomas Jefferson
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