The time limits take pretty good care of that, here. I really don't mind them watching braindead stuff for a limited time. Especially so if that's the price for watching something interesting too.
It's also slightly curated, with age limits on videos provided by YouTube, but I mostly care about that to weed out shock videos and extreme violence.
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.
It's also slightly curated, with age limits on videos provided by YouTube, but I mostly care about that to weed out shock videos and extreme violence.