Honestly, I don’t have a perfect answer. It really depends on what the service is.

My main thing is I want to be able to opt in or out of various filters. I don’t mind if my kids want to listen to music that has swear words, but I don’t want them watching videos where they give horribly sexist pickup artist advice.

This isn’t just about what I feel is age appropriate, either. It is also about what I know about my kids.

My 10 year old hates scary things, and she gets completely freaked out when they show scary movie previews. I would like to be able to block those for her. On the other hand, my 7 year old is obsessed with scary things and I don’t mind if he plays zombie video games.

> My 10 year old hates scary things, and she gets completely freaked out when they show scary movie previews. I would like to be able to block those for her.

The difference between this and the usual "parental control" mechanisms is that what you're describing here is something the child wants to cooperate with, voluntarily. In which case, you don't need a mechanism that makes it absolutely impossible; you need a mechanism for helping them not see things they don't want to see. That's something some adults also want (e.g. tools for preventing oneself going to Facebook, or going to TVTropes for too long).

I'm as a big of a horror movie fan as you can find, and I'm completely dumbfounded by the jump scares marketing is allowed to show in trailers nowadays. IMO (coming from someone who is basically unaffected by jump scares), they've gotten more shocking in the past couple years.