so i did jiu jitsu for 3 years , and now my brother and his wife have done jiu jitsu for 1 year , and the other day i was in shock when they enrolled my 3 year old nephew into jiu jitsu too ... omg the kids gonna be a monster 
It's always good to start them young! Hopefully they love it and stick to it.
i hope the kid stays with it too, it will give him a lot of discipline and useful skills in life like self confidense 
I agree. Kids can get a lot more out of sticking to those types of sports other than just physical exercise. It teaches them great personality traits like dedication and hard work.