Child swap may be a little different than the "parent swap passes." With the passes, you can actually just send one parent with the kid or kids in tow PLUS fast passes, and tell them another parent is waiting to go later. Then the CM (at the entrance collecting fast passes) will give you a child watcher pass, for the life of me I can't remember if that is the correct name. Then parent #2 can go on with 2 or 3 kids later, and they get to go in the fast pass line also. At least this is how it worked on our last trip, which was over 18 months ago.
I always thought Child Swap, just meant that two parents and a kid waited to get to the front. One parent went on the ride while the other parent and kid waited at the front of the queue. Then when the ride was over, the other parent got to go on.