[Lance is quiet, listening, but he's more watching Rosen's reactions; he can see easily how hard this is hitting him.
But the last comment is a little unexpected, and he wants to say that he doubts that, or even that he doesn't work with children for a reason, but he thinks a question is more useful in this instance.]
Why do you say that?
[He means it more in terms of why Rosen thinks he couldn't help Frisk as much as Lance could, not why he would think Lance would be able to.]
[Action]
But the last comment is a little unexpected, and he wants to say that he doubts that, or even that he doesn't work with children for a reason, but he thinks a question is more useful in this instance.]
Why do you say that?
[He means it more in terms of why Rosen thinks he couldn't help Frisk as much as Lance could, not why he would think Lance would be able to.]