I stopped with my motorcycle after only 1 year, and long before I had kids. Too dangerous, even just driving on regular speeds on regular roads. What really struck me is even if I had moved off just a bit to one side on the highway on-ramp, people in cars would try to pass me. On the frickin' single-lane on-ramp, even though I was going at the proper speed.
Plus, I only liked motorbiking in the late spring, early fall or on cool summer days. In the summer it was usually too hot to wear thick protective clothing, and early spring and late fall it's too cold. However, during those motorbiking friendly periods is also when I liked to cycle. Motorcycling lost out to bicycling.
I don't have kids, but if I did I would continue my passion (mountain climbing) and get them involved when they got old enough. I know several climbers who have done this...
I only do indoor climbing now. However, the main reason is the time factor. It's a lot easier to spend the time outdoor at the cliff when you have no kids. Also, I was never a big outdoor climber to begin with. Just did top-rope stuff outdoors. Kind of was a PITA to have to go there at 6 am to secure a few good runs and set up all the top ropes.
I may get my kid(s) involved when they get older though.
P.S. It should be noted that often times disability insurance will be more expensive if you do a lot of motorcycling or outdoor climbing.
MMA. I actually started after having kids. I've been hurt a couple of times and had to have surgery due to an injury. It is rare to actually die in the sport so I don't know if I consider it a dangerous activity.
You don't have to have a high risk of death for a sport to be considered dangerous IMO. I would most definitely classify MMA as a dangerous sport. Lots of potential for some disabilities. For example, I wouldn't recommend a surgeon take up this sport. Losing eyesight in one eye or getting a bad wrist fracture are both potentially career ending injuries. I suspect if you were a surgeon applying for disability insurance and told them you were an MMA fighter, they'd simply just exclude coverage for any injury sustained in that sport.