Have you tried creating a YouTube Kids profile? What you’re describing sounds like what they already have. It is not the default but there is a setting that allows you to create a list of allowed channels. The setting is called “Approved Content Only”.
YouTube kids is a wasteland for non English content. And also, there is whole world of content I would be more then happy to encourage my kids to watch that is unavailable there.
While also containing huge amount of unboxing toys crap I would not give to my kids in my own watchiles.
