Is respecting children a faux pas?

Some decades ago, during my college days (yes, I'm getting old), I accompanied a friend to his family gathering. I wound up engrossed in conversation with his stepsister J., age 15, whose knowledge and insight impressed me. At dinner, the three of us occupied a conversational niche at the middle of the table. The conversation at the table's end was the sort of speculation that often entertains dinner companions: The women of their parents' and grandparents' generations were taking turns sharing their explanations of some curious phenomenon. They took each other seriously, even though none of them had anything convincing to say on the subject. (My apologies: As much as these events have impressed themselves upon me, the intervening years have been more than sufficient to steal the subject itself from my memory.) A slightly heated debate ensued. At an appropriate gap in the adults' conversation, J., who was seated at their edge, made the usual gesture to draw attention. She began to submit a solution to the question under discussion, in the simple, explanatory tone of one who knows the answer. The adults avoided eye contact with J., and one of them immediately started talking over her (not to her; only to the others), so that they did not hear more than three words from her. It was smoothly done, as if J. had merely tried to interject during an insufficient pause. She politely waited for another pause, and was then interrupted in an identical manner. After the third time it happened, she gave up.

( The rest is behind a cut for the sake of your feed, but you know you want to read it. )

All right, I'm getting sidetracked. tl;dr: I like to show respect.