So I hash some combination of ID, name and birthday and send it to Facebook to create an account. Facebook relays that hashed info to a government server which

So I hash some combination of ID, name and birthday and send it to Facebook to create an account. Facebook relays that hashed info to a government server which responds with a binary yes/no. Of course you need to trust that the hash is not reversable. That doesn’t stop kids from using Facebook, but it stops kids’ ID from being used to create an account.