Does the following technique work?
Here is a tip for getting the most out of the fastpass line if you have small children with you. We arrived early in the day at the Magic Kingdom and went straight to Space Mountain when the wait was only about 10 minutes. Go up to the fastpass entrance and tell them that you need to do a child-swap for the ride. They will give you a ticket that allows up to three people to enter the fastpass line. The ticket is good all day, so don't use it right away when the lines are really short. Have the person/people that stayed behind with the kids go through the stand-by line and save the fastpass ticket for later in the day when the lines are over an hour long. This worked for us on just about every major ride at all the parks. We also had pretty good luck getting a fastpass, then going up and telling them we needed a child-swap. Get the ticket and wait a little while before going in. Use your fastpass ticket that expires within an hour at that time, and save the child-swap fastpass ticket for later in the day."
Here is a tip for getting the most out of the fastpass line if you have small children with you. We arrived early in the day at the Magic Kingdom and went straight to Space Mountain when the wait was only about 10 minutes. Go up to the fastpass entrance and tell them that you need to do a child-swap for the ride. They will give you a ticket that allows up to three people to enter the fastpass line. The ticket is good all day, so don't use it right away when the lines are really short. Have the person/people that stayed behind with the kids go through the stand-by line and save the fastpass ticket for later in the day when the lines are over an hour long. This worked for us on just about every major ride at all the parks. We also had pretty good luck getting a fastpass, then going up and telling them we needed a child-swap. Get the ticket and wait a little while before going in. Use your fastpass ticket that expires within an hour at that time, and save the child-swap fastpass ticket for later in the day."
I suspect, though, that these abuses will result in more and more restrictions and limitations placed on child-swap over the years. When that happens, folks shouldn't complain about Disney "ruining" child-swap, but rather should blame their fellow guests for having exploited every avenue they could, forcing Disney to take such actions.

