I'm honestly at a loss for why the whole "children of her body" thing implies that Jon is Ned's son. It seems to me that "children of her body" could mean two things: 1. the children who came from her womb, or 2. her biological children in general. If it means the former, then the phrase "children of her body" can really only apply to Catelyn, and thus has no application to Ned and Jon. If it means the latter, then it could also apply to Jon and Ned; in other words, Ned could refer to Jon as a "child of his body," given this meaning. However, Ned never does say or imply that Jon is a child of his body. He never once asks himself what he would do if he had to choose between Jon's life and the life of another child. That is rather telling, IMO.
As for why Ned uses the phrase in the first place, I always assumed it was just for emphasis, as I see no other purpose for it in the sentence.
EDIT--Nevermind, wallofice hits on a perfectly good explanation. Jon is in a sense Catelyn's son, or at least her foster son. So if Ned said to himself "what if Catelyn had to choose between Jon's life and the lives of her children," that would probably seem a bit...imprecise, in his mind at least. By saying, "what if Catelyn had to choose between Jon's life and the lives of the children of her body," he's distinguishing between Catelyn's biological children and her foster child.
The whole "Incorrect" thing was meant to be succinct and attention-grabbing. Also, I honestly believed you were incorrect. You were making a claim that the grammatical structure of the sentence implied that Ned thinks of Jon as his son. I believed that was incorrect, and you have yet to challenge my argument on that front. If the way I expressed myself came across as condescending or arrogant, then I apologize.
Edited by Dragonfish, 01 July 2011 - 05:50 PM.