And that's the point that I don't know, because I have not seen the information. IF the parents boarded with just the toddler, and the 3rd seat was originally booked for oldest son, then from the airline perspective, it is a spare seat for the no-show oldest son, and youngest child never had a...
Maybe there is a bit more to this?
If husband, wife and two kids originally book 3 seats (youngest to sit on lap) - then oldest kid flies ahead on a different plane - then from the airline perspective, the oldest kid is a no-show and there is a spare seat that they can put a fare-paying...
Shocking and indefensible attitudes and actions by airline staff.
What surprises me is just how thin the airline margins are, which leads them to almost routinely overbook a flight - https://techcrunch.com/2017/04/11/overbooking/
Given the above, it is maybe surprising that this kind of scene...