I have been using child swap for years with my kids (first with DS8 and now with DS1). 95% of the time, the required the little one to come up to the entrance and they definitely looked at him to make sure he wasn't tall enough. We didn't like crowding up the entrance area while others were pushing past while the CM dug around for the swap pass, so sometimes we had the stroller and non-rider off to the side a bit. They always asked to see him. You may get lucky, but most likely be prepared to not get a swap pass.
I would suggest booking FP+ for all 4 of you on the ride. Then DH & DS go through with FP+. Then when they get off, have DS use DD's Magic Band to go back through with you. Basically will work the same as using the Child Swap pass.