The reality is that most of the "I would never trade my seat, don't even ask me you over-entitled jerk" talk is just posturing. The reality is that real people, in the real world, are generally very reasonable (sans the "will you trade me your exit row aisle for my middle seat in the lav" requests). Even more so, real world people (and many here are likely real world people when actually out in the real world) will bend to help a parent with young kids.
As I said, we've been declined just once in quite a number of polite askings...and we're just a basic middle-aged couple. Real world people are usually glad to help.
Cheers.
^
I suspect that the difference is that you don't threaten, bully or cajole. A polite request such as yours is going to yield better results than a demand.