Robb did not need to cast so much as a glance in his father's direction to know the expression that he would find on Ned's face: hard, unwavering, and grim. He knew that his father would only be even more on the defense than when they'd entered the room, after Stannis addressed Robb without any hint of respect. Robb hadn't expected deference, of course, and was unsurprised by the curiosity that was so evident as Stannis approached and greeted them. He also did not miss the fact that Stannis still regarded his father as the Stark in charge of this meeting - indeed, after the events of the Red Wedding and his miraculous return to Westeros, there was little that Robb could afford to miss.
"Lord Stannis," he intoned with a solemn nod, removing his hand from the hilt of his sword as the doors closed behind them. "Despite what you may have heard, my father remains Lord of Winterfell and only attends our parley by my own invitation. Your business remains with me." You would do well to learn that, was his unspoken warning. One look to his father would only confirm this. Robb's own men knew him well enough that he need not worry about disrespect; they had seen him in battle and they had seen him treat with their enemies enough that he had earned his title in their eyes. Robb had no intention of allowing Stannis to treat him as a child, though he had foreseen this particular struggle.
Robb moved farther into the room as he gazed around with interest, having noted almost immediately the lack of any valuable information that was to be gleaned from the room's contents. It was a smart move, to be sure - and all the more cause to trust that Stannis knew what he was doing.
"Indeed, it seems to be in both of our best interests to come together as allies. As King in the North, I swear to you that me and my men have every desire to see the rightful king on the Iron Throne. The bastard boy has no place in King's Landing."