A Trade Worth Making: A Baby for a King

Sitting around the fireplace, your grandfather tells you the tale of a girl named Sarah, her infant brother, the Goblin King who granted her wish and took him away, and the labyrinth. As you listen, you can't help wondering if you can actually make such a trade. As you ponder this you come to a startling realization; if given the opportunity, you would do it in a heartbeat. Looking up at your grandfather the one thing you need to know to make this trade......what are the magic words.