As for Henry–perhaps he has magic like Emma? Oooh–since the Queen had to kill “the thing she loved most”=Henry Sr., to enact the curse, perhaps young Henry must be sacrificed to undo it? After all, if the curse had never happened, Henry never would have come into existence. Then again, I can’t see Disney killing off a kid–so maybe he’s the “key” in some other way?.
Wait, you’ve lost me here, doesn’t Emma already broke the curse? So why Henry should be sacrificed to undo it?