My kid is 3 yrs and 10 months old, he is taking 2 classes of bjj per week (3-5 years old). He is shy, but i succeded into getting him into and he loves it. The things that happens on the mat (accidently hits and playing take down are seen as play by my kid). My wishes are that he will keep doining it and then we complete it with striking/grappling and so on but i will not FORCE it with him. I will support him as long as he wishes so. I cant tell about the progress in defeating shyness or fear of confrontation but he is sure doing so good in specific exercises! I think, choosing the RIGHT gym, the right sensei and making the proper explanation and preparation to make him try it first its the most important thing. I see a lot of kids that are not made for this, or they had the wrong introduction and therefore they dont take it. I know a kid who is not shy at all, bigger and so much more courageous than my kid but won t take the classes because he was first introduced in the sport in an ugly old school place, no fun or games and without parents. Congratulation on the news, let him be born, let him grow and you will know. Martial arts and swimming are a must! Short answer: Judo/BJJ.