death to capslock

The Leaky Cauldron situation is consistent with the 12GP one: There was a Fidelius cast centuries ago, the Secret Keeper told everyone trustworthy. Secret Keeper died - suddenly hundreds of Secret Keepers, who each can tell the secret to anyone they chose. And when each of them died, all those told by that person became Secret Keepers. So Harry becomes a Secret Keeper of The Leaky Cauldron when Hagrid dies. His kids don't have to wait that long though if the version of the Hogwarts Letter that is sent to children from wizarding families contains the secret.