The king came up with the idea of marrying his cold, cruel, merciless and son to soften him up. Although Childe don't want with this, he didn't want to go against his father. He said that at least he wanted to choose his own wife instead of marrying stupid princesses. The king invited all the young girls to the palace, everyone was trying to attract the attention of the prince, but no one succeeded. You weren't trying to get his attention anyway, because you knew you couldn't.