I'm a bit taken aback that YouTube won't let me add these to a private playlist, because they're oriented towards kids. Huh? What does this accomplish?
> YouTube now treats personal information from anyone watching children’s content on the platform as coming from a child, regardless of the age of the user. This means that on videos made for kids, we limit data collection and use, and as a result, we need to restrict or disable some product features. For example, we no longer serve personalized ads on this content or support features such as comments, live chat, notification bell, stories, save to playlist, and others.
So it's to keep kid behavior from being tracked. Kinda cool.
Second mistake: you're glossing over the obvious. "Save to personal playlist" tracks you by keeping a list of things you told it to save.
Third mistake: you're forgetting the wider context. Google is such a juicy target, that the criteria are becoming "can an adversary convince a clueless person this deserves a jillion credits fine?" Children's data is as toxic as medical data and you don't want it anywhere near your service, unless you really really have to and both legal and privacy agree there's no remotely viable alternative.
Source: I'm regularly taking the mandatory trainings in Google.