If the younger keeps getting hurt but still wants to wrestle, I would probably try to teach them the actual rules of wrestling (at least the ones designed to keep people from getting hurt). With a a rule structure, and even a points structure, I could see the wrestling getting a lot more fun and a lot more safe... of course there is a chance they will hate the structure, but it is worth trying IMO. There are also different styles of wrestling, some of which are very injury resistant,
Greco Roman does not allow you to use your legs for any hold or contact with the opponent except for incidental contact related to positioning (basically you can only use your arms and arms are a lot weaker than legs).
Freestyle is primarily based on "throws" and rolls, if TV style "professional wrestling" had a real world equivalent, Freestyle would be the closest to it, and it is definatly the most dangerous.
Collegate wrestling is the most common in high schools and colleges, it focuses on pins and holds (the only way you can get points is to pin or come close to a pin). This is a compromise between freestyle and greco. Still more dangerous, but much easier to understand than greco, but loads safer than freestyle.
There are other styles of course, such as samba, but that is even more dangerous than freestyle (but even cooler hah).