YT Kids (the app at least) has a setting where only videos and channels are allowed that are whitelisted by the parent. We used to limit it to stuff from BBC Cbeebies, Numberblocks & Alphablocks, Sesame Street, Disney, and similar stuff in their own language and in English.

I think nowadays we just limit it to the age restrictions (<=4, 5-8, 9-12), so they don't see stuff that gives them nightmares. Everything else can be taken care of with the time limit.