YouTube Kids, which is a separate app on iOS and Android is a customised, pared back experience for kids which provides a safe environment for parents to give to kids and be safe in the knowledge they won’t see anything age inappropriate by accident. The service uses humans to review the content, feedback from parents as well as automated filters. Parents can even restrict screen time in the app too.
As of the 27th May, YouTube Kids is now available on the newer Apple TV models, the HD and the 4K models. (HD is the fourth generation and was launched in 2015, 4K is the fifth generation and was launched in 2017.)