I see so many of these complaints about YT having lots of good family-friendly content but at the same time being terrible at curation even in the kids mode.

Seems like the problem can be solved with a crowdsourced list of family-friendly videos (on GitHub?) managed by trusted collaborators and then a simple page that embeds only these videos?

Over time I assume it should work given enough people contributing. It's not like the content needs to be kept continuously up to date either (unless old videos disappear faster than new ones are added).