I think the issue is, as others have said, that the family was used to being treated a certain way with the child. The little girl is small, so there were probably many times that the FAs just assumed that she was under two, so it might have never come up. I’ve flown with some things not in the plastic bags as they should be and luggage over the size it should have been to be carried on, and not gotten called on it. But that doesn’t mean that if I am caught, that the fact that I got away with it in the past, means that I get a pass. Could happen. Might not. I think that the mom was so used to not getting a second glance with the seating situation that when it arose,she got insulted and upset.
The other thing that I think that might have been an issue was that they were sitting in upgrades seats. If they had been sitting in steerage with a kid on their laps, it might not have caught anyone’s attention. But when one sits in first class, business class, or whatever and there is a child on your lap, that can be an extra flag. It would be a flag if there is an empty seat next to the parent for the child and she isn’t in it, and it could equally be a flag if there is no seat for the child. A request for the boarding pass for the child (to check age or whatever) that showed the child’s seat to be elsewhere could have started the whole thing.
A confession: in the days of yore, I used to always bring my little on the planes on my lap as long as I could get away with it, even beyond age two. Dangerous, unethical, etc, but many of us did so. One of mine was small enough that he looked like he was two long past his age, and we did take advantage of that. His younger brother was a big fellow and was questioned about his age even before he reached two. But that used to be something many of us did. With just one child, I used to drive 12 hours one way to check on my mother with a baby in the car. Leave on Friday, come back on Sunday, with sometimes an extra day if I could manage it, which was not a safe situation either, driving that distance alone with a child. Couldn’t afford the airfare then. When we finally could, there was another child and he went on my lap for many years when we traveled. I would not do it now, nor would I advise it, but the reason for doing it was that I felt that the risk of a serious problem was small enough that I was willing to take it. The same reason the airlines permit this for children under two. it really doesn’t matter if the kid is under or over two from a safety perspective, but the size is what counts.
I don’t have any rancor for the mother and I don’t think she was trying to sham the airline. She’d just been used to doing things that way witht he child up to the point that she felt she as entitled to the exception and that it was unreasonable for the FA to refuse to let her do it again. There were a number of FAs involved, and one can see that only one out of the four was looking at it as an issue. Though that one was right–it was regulation, it leads to resentment when expectations are broken that way. What the captain , the airline, the FA, all should have done, was gently explain to the woman, that the problem was that the others had not enforced the airline’s regulations in the past, which happens with a lot of thing, but that the rules were in fact as stated, and apologize for the expectations that were developed from not enforcing these rules more stringently in the past. Once the case was identified as a breach of rules with a possible safety issue, the airline really could not take the chance that some fluke accident occurred and they allowed the situation to remain as against the rules when they knew it.