This isn't a single issue, and your view seems excessively simplistic. Kids are gullible. Kids keep secrets for any number of reasons -- and while I've taught my kid that strangers insisting he keep a secret is a major red flag, if a predator convinces him that they're a peer, they might enter the "friend" category when an adult would still call them a "stranger." Also, what kids and parents consider to be noteworthy can differ by a mile. How do you (a) enforce an ironclad rule that the kid tells you everything about every new contact and status update and (b) maintain the kid's trust? You don't, that's impossible. Yes, parents have duty to educate their kids and engender a trusting relationship, but every child is an individual who develops autonomy (by definition) before they're ready for it.

I have a friend who was catfished in high school, and the fisher took on a persona for several years before "introducing" her to the fisher's "friend" who was actually the fisher -- and he maintained the ruse for several years after. I'm honestly unsure of how a parent could even prevent something like that. The only comfort I've got today is that video chat is normal and a friend who couldn't do that would probably noteworthy enough to mention. That comfort is diminishing: by the time my kid will be old enough to worry about, deepfakes will be that much more advanced.

I think you underestimate how children overestimate themselves. I have an exceedingly good relationship with my younger siblings and they will think they can handle situations beyond their capacity, and then when they bring me in sometimes the emotional or psychological damage has already been done.