NBC’s American Ninja Warrior began as the late G4 network’s translation of the Japanese competition event Sasuke as Ninja Warrior and started as a contest to compete in the Japanese version. It became popular enough that it eventually became a US spinoff in cooperation with NBC. Japan has also had an all women version called Kunoichi, released in the US as Women Of Ninja Warrior (which has not been done in the US version, who instead has a mixed gender exclusively, though women can compete in Sasuke) Once they did an all kids version but that was never released in the US to my knowledge and I don’t think that happened more than once.
NBC Universal on the other hand is ready to break out their own kids version of American Ninja Warrior, to air on UKids (Universal Kids). I want to see this. Outside of the recently returned Double Dare and the rather disappointing Gladiators 2000 I don’t think there’s been a decent kids obstacle course show since GUTS ended. The show is very popular with kids in the US so I think creating a kid-safe version of the course is a good idea. And I probably couldn’t handle that one either.