I didn't mean the second one gets off the ride, I meant as soon as they get back to the swap area. There are no lines anywhere that allow you to stand on the loading platform. I thought that was a given & didn't have to explain about walking back to the area. My suggestion was as opposed to just using FP and having to wait on an FP line. Do they not have waiting areas for the swap? Disney use to & Universal I know still does. As far as entering a line without meeting the height, if you tell them you are doing baby swap, some give a pass there & others allow you to walk thru with the rider & exit just before it as in the case with Space Mt. I know they let you out just behind that bubble area where the CM's sit & watch, just beyond where the turnstiles are. The one with the children leave and the rider then goes left or right.
No, there are no "swap waiting areas". You posts inaccurately describe how the current Rider Switch works and that's why the OP is getting confused.
Do you plan on doing the real swap, if so you will need to stay together until you reach the swap area. Then each of you take turns waiting in that area without having to enter the line again.
I was going to say this too, but then I thought that by doing it this way, they will each need to wait on a line for each ride. Even with FP, there are lines to wait on. It goes much faster if the other parent can jump on as soon as the 1st one gets off.
Each parent must go through a line (either FP or standby) and they will not allow you to "walk through" with the baby to wait to do a swap. They give you a Rider Switch pass before the first parent enters the line and the other parent and baby are free to do whatever they want while waiting-- stand near the exit, do another attraction, get a snack. When the 2nd parent wants to use the Rider Switch pass, s/he must go through the FP line.