[oakashes]

The ability to make all content opt-in instead of opt-out would get you 90% of the way there. Very few services that I know of offer this. Most of them offer gating by age range into all content the service considers appropriate for that age, and most allow you to block specific content as well, but all I really want for my young kids is to know exactly what content is available to them because I have added it specifically.

Beyond that, there are some nice things you could do like a workflow for a kid to request new content and a parent to review and approve/deny it. But that's definitely a nice-to-have.

[cameldrv]

This. There is some fantastic stuff for kids on YouTube (most of it though is actually made for adults and is not available on YouTube kids). However, there is a tremendous amount of trash, and the recommender loves it. I wish I could add a bunch of good channels and let the kids pick their own content, but only from that list.