For small kids they are just so ridiculously resilient and light. Injury rates before teenage years is very low in my experience. They also only go 2-3 times /

For small kids they are just so ridiculously resilient and light. Injury rates before teenage years is very low in my experience. They also only go 2-3 times / week maximum and the coaches keep the training intensity moderated in the younger kid's classes. This matters a lot. As an adult, I won't lie, BJJ hurts some times. Common injuries are finger/hand/foot/toe injuries. You will definitely get bumps and bruises, some times significant ones, but that is no factor usually. If you aren't in good shape you are at more risk. It kept me away from the practice for a long time, but... you modulate your own BJJ experience as an adult. Go less frequently and choose the right school, it is a journey like anything else. I personally have subluxated my ribs once (really only stopped me from doing BJJ, I could still run/lift), but it really hurt, and my fingers and toes definitely feel it some days, but nothing that required a doctor yet. The up side is... it is one of the most amazing things I have ever done. It keeps my ego in check. It is as intensely technical as you want it to be. It is like the merging of an ultimate nerd and fitness hobby into one martial art / sport. It is a legit martial art. If you start training seriously, I think it requires a serious training focused on improving your strength and muscle mass for injury resistance as well.