We still never settled the question of exactly who was the great authority that originally deemed that younger people automatically giving up their seats to any one over college age was "good manners", so that generations later we must all still automatically obey this unquestioningly?
I can certainly see some circumstances where it would make sense for a young healthy person (child or adult) to give up their seat for someone who was frail, ill, permanently or temporarily disabled.
I can also see many circumstances where it makes no sense. For instance, what if the adult in question is fit and healthy and the child is frail or disabled? What if the child was just tired and hungry and had a long day and needed to sit down. Children, for all their energy, often tire quite quickly. Why should we just assume that the adult's needs supersedes the children's needs.
What if the mother had a long day with all her kids and wanted to sit in the nice comfy couch? Perhaps she had never been taught by her parents about this universal rule you speak of about children automatically giving up their seats as a sign of politeness and reverence to adults they don't even know. Perhaps her own parents taught her it was first come, first serve, for seats in public places (which indeed, is the pervailing policy in most places) and that it was rude of others to not wait their turn before expecting those who were there first to vacate them) From her perspective, (which was constructed by the environment she was raised in), she may not have thought she was rude at all, but may have thought FHN was rude.
Who is the ultimate authority in society who decides what is good manners and what is bad? Really, manners are fluid and change in time and context. Historically, it has been those with political, financial and social power who decide what is proper behaviour. The traditional power heiracharcy in the south has been white men, then women, then children, then blacks. That was the pecking order of respect in that society in the past. At one time it was just assumed that a black should give up their seat for a white and that any who refused were being grossly disrespectful and needed to be taught some manners with a good beating. Well, thankfully there has been progress on that front, perhaps in another 100 years we can also emancipate children from archaic notions of respect. :-)
Because a certain behaviour has traditionally been a sign of respect to those in greater power it does not automatically confer some sort of moral rightness on the behaviour, even if it is a matter of law. As long as we rank people in society in degrees of respect deserved, we will always have these kinds of debates. Here's a novel idea. All people in society are equally deserving of respect. If we start with that premise, then on a case by case basis, depending on the context of the situation at hand, it will be readily apparent how to act in any given situation. We need to question our assumptions about others and investigate further, not jump to conclusions reactively.
In case you think I am siding against FHN in this debate, I should state that if I was the mother, I would have graciously given her the seat in that situation and gathered my children closer to me if I didn't want to send them to the children's section. If I were FHN in this scenario, I would also never just assume that the children should give up their place for me because I was an adult. However, if the child wasn't actually sitting in the chair at the time, and I was tired and wanted to sit down, I would have just sat there; I certainly wouldn't have asked the mother for permission in a public place thereby conferring on her some sense of authority to commandeer or reserve chairs. You snooze, you lose. Does that make me rude or polite? It depends on the time and context.
Cog
ps: I was always taught it was the height of rudeness and bad manners to insinuate when a woman didn't agree with you in a debate it's because she must be premenstrual or menopausal. But hey, I'm not from the South, so what passes for politeness down there could be very different from in Canada. Now I know Scully also made fun of FHN's avatar, which could arguably be said to be rude, but since she was arguing the premise that respect is earned, not demanded, I can't really fault her logic for that one.
pps: I actuallly LOVE Miss Manners and read her all the time. She has a very common sense approach to etiquette that allows when tradition no longer makes sense, then discard the tradition.