The Stark and Salvatore children grew up together, side by side. Stefan's siblings had befriended themselves with the eldest Stark boys, so Stefan was left with the daughter, Sansa. If he ever felt bitter about the arrangement, he never said so. Perhaps she wasn't as adventurous as the young boy would have liked; he could not tempt her to run through the woods, jump into muddy puddles or to climb trees. None the less, he was endlessly fond of her; he would cherish the sewing she gave him, he would be enraptured when she sang to him. They were sweet children, with a sweet friendship.
When he was told of her betrothal to Joffery, he was as thrilled as she was. His dear sweet friend would be Queen, and she had her dear sweet prince. Stefan was too young to distrust the Lannisters so, too young to know how terrible it would be to leave Sansa in their clutches. Then the day came, where they all had leave their childhood behind and face the wars and harshness before them. For the love that he bore for his sweet dear friend and her blood whom he cherished as family, he would return her to Winterfell.