Lyanna Stark had twins instead of one child Jon and his sister Jasmine. The stories about Rhaegar Targaryen kidnapping and raping her are true but Rhaegar didn't just kidnap Lyanna he took her away from her husband Jon and Jasmine's step-father Mance Rayder. On the night of the feast between Lannisters and the Starks Benjen and Ned tell Jon and Jasmine everything and tells them that he and Ned and their cousins love them but think it's time for them to be with their father.