Yeah, I remember reading a lot about those playlists, and I understasnd that can be pretty disturbing or upsetting if you as a parent assume that a playlist is "safe".
However if YT already has the ability to mark videos as for kids-only, I have no idea why wouldn't they be able to restrict playlists that contain even a single video that is not kids-only.
I.e. if you want to have a YT Kids' playlist, then all videos need to be YT Kids.
But the other way around (i.e. a regular playlist with some YT Kids videos) seems irrational.
However if YT already has the ability to mark videos as for kids-only, I have no idea why wouldn't they be able to restrict playlists that contain even a single video that is not kids-only.
I.e. if you want to have a YT Kids' playlist, then all videos need to be YT Kids.
But the other way around (i.e. a regular playlist with some YT Kids videos) seems irrational.