Originally posted by NotUrsula
My personal impression has been that other passengers will not care if you save seats *within a row* that someone is actually sitting in, so long as someone eventually boards and sits in that seat. Putting personal items in entire rows in order to mark them as "saved" is frowned upon as bad SWA etiquette, so to speak.
(Trying to save a seat for a "passenger" who doesn't exist in order to get yourself more space is an evil deed.) Normal saving technique for 2 seats is for the saver to sit on the aisle, saving the center and window of the row. When people ask, it's more polite to say who you are saving for, rather than just chanting, "it's saved." "I'm holding two for my husband & child" is a much more acceptable motivation.
There is something of a culture that has grown up around SWA's boarding process. There are things that everyone does that are accepted, and then there are things that will earn you lots of dirty looks, or even intervention by an FA. Saving 1-2 seats is OK, but saving 5-6 is overkill and may be stopped by the FA. If you can avoid it, don't try to save more than 2. If you do have to save out of another row, try to leave the aisle seat open.
US law requires a child who is under 5 years old to be seated with an accompanying adult, so that is why SWA preboards only up to that age. Children 5 and over are, by US law, old enough to fly as unaccompanied, so there is no rule that they must be seated with an accompanying adult. FA's can force someone to move to get an under-5 seated with a parent, but they cannot do that if the child is older. They will ask for volunteers, and perhaps sweeten the pot with free drinks if no one comes forward, but that is all they can do.
The best thing to do is to try to get there early enough to make trading unnecessary, but if you anticipate having to trade, try to snag an aisle seat for the adult and put the child in a middle seat; people will be more willing to trade into an aisle seat. Try to avoid the row in front of the exit or the very back row; those seats don't recline, and it is very hard to get anyone to trade into them. Usually someone will quickly volunteer to trade; the only situations I've seen where FA's had to really beg are when the new passengers are connecting onto a weekday flight that is already full of business travelers. This is the dreaded "connecting flight with nothing left but middle seats" phenomenon, and it is, thankfully, quite rare.