Is it annoying though, even if they're not strictly bothering others. I mean, you pay good money or use major amounts of miles to sit up there. Why should someone else get the same for free?
For the record, that was a FAA violation IF it took place on a U.S. company. Passengers from the front can go to the back but not the other way. I'm curious if it was a U.S. company because both I worked for didn't allow families to split up this way. Perhaps they got around it by booking a child and a parent up front and then the rest of the kids and the other parent in back, then did a flip. That too, would have not been allowed.
Someone said that the Flight Attendants had a choice. We didn't. We didn't have the authority to move anyone between classes, although that could be done on the ground with the agents' help. I did upgrade someone once. We had a way of doing it at top dollar. I won't go into details but it was kind of complicated and we had to have the captain's permission. It was only because I remembered learning about it in training but that was the only time I put it into action.
Nationality doesn't really play a role except, an observation: in some countries, only the very elite have enough money to fly, the very same people who can afford full time nannies. So what happened wasn't some fault of the person's background, country or whatever but I was observing a parent who simply wasn't used to taking care of their child(ren).
Some parents brought grandparents and nannies to help out but some were alone, making very long trips, clueless about what their child needed. I saw parents who hadn't packed any snacks or toys, for example and children dressed in stiff, formal clothes for long haul flights. If the nanny back home got sick, the parent would be taking care of their own children in their own home but at 30,000 in a crammed airplane, it was tricky. Flying is tough even when you do know all your childrens' various whims and needs!
A letter to the company is in order. Don't even mention the nationality but try to remember what seats they were occupying.