This post really hit home. I had to call my husband into the room to read it to him. This was our story from last July. We were also staying at the Poly and wanted that one night out. We have 3 children. DS was 3 3/4 at the time, DD8, DD11. We were not worried about leaving our son since his two older sisters would be there to keep an eye on him. Well, I knew ahead of time that he had to be 4 from doing my homework, but knew he was well potty trained, would love to go with his big sisters, etc. So I called and made the reservation several months before the trip. The they took the names of the children, but didn't ask ages. When we checked into the Neverland, they asked the ages of our children-they already had a form filled out with their names and ages on it. They asked how old Michael was? We knew they knew, so my husband said 3. They said they knew this because the reservation was also tied to our orginial disney reservation package for park tix, dinning, and our stay at the Poly. We just figured that when the Disney Reservationist took the reservation they had to see the ages as well. The staff said they would keep him for the evening, but that they have a strong rule that they must be 4. I played dumb and mentioned that he they knew he was 3 why didn't they call and inform us as they already had our room #. They never really responded with an explanation. So we left the kids and gave it a try. They gave us a beeper as they do all parents, but to be honest I couldn't relax after we left them because of this. When we returned the staff commented on how well behaved our son was and that had no problems with us reserving another night during our stay to leave the kids at the Neverland. Go figure!
So I really can't tell you how to handle it, only that I know exactly how you feel and that we did try it, did get caught, but then did leave our son stay, and then Neverland Staff offered to keep him another night. Like I said 'Go Figure'. I wish they would change the rule to potty trained 3 year old allowed with older siblings because I think that makes all the difference in the world. We would have never tried to 'sneak' our almost 4 year old in if it would have been just him, but with his older sisters we were not worried.
Have a magical vacation whatever you decide!