I coach kids boxing, it is a very positive space, no hard men because at some point (and soon) every single one will get humbled. Not all gyms are as friendly, but in my experience most are very nurturing places. There is no picking on the small kid with your mates to back you up, or running away if the victim catches you with a good shot.
doesn’t have to involve being able to handle yourself though
in the last 2 weeks my kids have been waterskiing, sailing, zip lining and many other things they did not want to do in tje moment so had to be pushed hard to get them to try. Every single push outside their comfort zone is an uncomfortable challenge BUT becomes another building block in their confidence
even simple things like getting them to order their own food in restaurants or drinks at a bar all helps
too many parents do too much for their children these days imo
also keep then away from x box and other such devices - they are the root of all evil in kids today and turms them into shy, mindless zombies