I don't see it as "just wanting to change seats" in my case. It's for the good of everyone in First Class. Our kids (4 and 6) will behave great with one of us sitting next to them, but if they sat by themselves without close supervision for 6 hours, they would probably be a little disruptive.

If it were just me and my wife and we were separated in the upgrade, it wouldn't be a problem. We would wait until we were on the plane, take our assigned seats, then explain that we got separated and offer our best seat to the the passenger next to the other seat. And if they said no, we would be fine.

I'm probably making a bigger deal of it than necessary. I'm sure one of the two passengers will be more than happy to swap seats. I can't imagine anyone who would rather sit next to a kid, separated from his or her parents (and their supervision), rather than switching from an aisle to a window (which is the only negative part of either swap) possibly with a seat that reclines better.

I just want to take care of it before we get on the plane so we don't cause any delay during boarding.