I just read through 40 or so Haggadot and, while I have a provisional (common sense) answer, no one seems to address this, so I appreciate any "real" sourced answers.
The fourth question (current day, Ashkenazic minhag, as opposed to the Sephardic order and the no longer used question about roasted meat) asks
שֶׁבְּכָל הַלֵּילוֹת אָנוּ אוֹכְלִין בֵּין יוֹשְׁבִין וּבֵין מְסֻבִּין, - הַלַּיְלָה הַזֶּה כֻּלָּנוּ מְסֻבִּין!
(text from here)
My rough translation/understanding is
That on all (other) nights WE eat "between" (meaning using either position) sitting and reclining; on this night "we all" recline.
I am trying to understand the exact meaning of "kulanu" "we all" in the explanatory second part of the question.
Is the child saying that "we all" means that we do ALL of our eating in a reclining position? Like the question on dipping, he cannot know what will be required throughout the meal in the future -- he should be asking only on what he has seen. However, he has seen one instance of dipping and sees the other ingredients for dipping and can infer that there will be another dipping (this is the answer I read in a Haggadah). But the child has not seen much eating (for Karpas we specifically eat less than the shiur so that doesn't seem like a substantial thing to infer from), only drinking so he can't infer that we will lean for ALL the eating.
And, if he did infer that, he would be wrong. We don't recline when eating maror!
Is the child saying that "we all" means that everyone reclines? The language conspicuously changes from "anu" (we) to "kulanu" (we all) so it might follow that this is about including all the people at the seder. This would make sense because he, the child, would have just reclined even in the presence of his father so that would seem unusual. But a student does NOT recline in the presence of his Rebbi so we don't "all" recline.
It is easy (and common sense) to assume that the child would not know this intricacy of halacha, but the child already has shown that he knows laws of maror and dipping before they happen so it seems wrong to assume that he didn't learn the laws of heseiba as well.
To what does the "kulanu" refer and why is it presented as an absolute when it doesn't seem to be?
Any insight would be appreciated.