In an attempt to bring peace to the world for the new year the Seelie and Unseelie negotiated a treaty. It took several days to work out the terms of the truce. The Seelie worried that the Unseelie wouldn't stick to it. Unseelie weren't known for keeping their word. So there had to be something that made them hesitate and reconsider their actions. So it was suggested that each Seelie and Unseelie give one child to be married to the other side. This way the scales would be balanced. No archnemesis would be bound. And no one would know who was marrying who until their wedding day. These would also insure that the Fey didn't fade out.