When they were young, you had a choice between YouTube being completely locked down with no option to whitelist channels or letting them watch almost anything (although I think this has changed since but it's too late now for those of us with children that age).
Now, there is no way I can whitelist contact/groups on WhatsApp or Discord servers/friends. Once they hit 13, pretty much any option to restrict anything feels taken away from you as a parent.
Luckily, I have sensible children (I think!) but it's really hard as a parent trying to both be reasonably responsible, but not deny all technology, it's really hard to navigate a sensible course.