Even if Facebook requird such a thing, children could just lie to sign up. It’s fairly common.
Isabelle
1

This is a hypothetical to insinuate that Facebook could require a notarized letter to affirm guardianship rights to sign up minors for the service and formally establish this supervised relationship status to between minors and guardians.

Given that Facebook’s real name policy is generally enforced, we could imagine parents being offered a lot more sovereignty over putting their kids on Facebook, especially if the notary requirement was upon sign up of minors, who would then need to be connected to at least one verified guardian.

Contrast this possible scenario to their ad-privacy settings today and it becomes clear that parents haven’t yet realized how much of their authority needs to be reclaimed from Facebook.

Lying about age when you signup for Facebook is an enforceable loophole that they could close if they chose to. We know this because when they require a notarized letter to opt out of ads it proves that the company is willing to interface with other bureaucracies and authorities if it deems it a necessary and good business practice to do so.