User blog comment:SummerandBran/Howland Reed/@comment-30471248-20161113200639

In the history, lyanna saved howland from bullying squires at harrenhal. Include the fact that cat and Ned were only married a year before he joined with Robert in his rebellion, it would appear that he would trust howland more than cat at the time. As far as Ned knew, the few people who knew about Jon snow, the better.