Try to keep things light since you'll be walking around each park a lot. Keep the gear accessible for the security bag check at the entrance of each park.
At a bare minimum, I would be taking two lenses unless you have an 18-200/250. One to cover the wider angles and one to cover the telephoto. If you want to be creative and bring other lenses - I would recommend the wide angle variety vs. tele.
One other thing I would recommend you to bring is a peachtree dust blower - that thing bailed me out when I discovered dust in 10 of my shots right after a lens change.
I went to WDW in May and brought my K100D. I was using my 80-200 most often in the Animal Kingdom. I also used the tele in the Beauty and the Beast theatre and Fantasmic. Most other places, I found myself using the 18-55 or my fisheye.
If I was restricted to one lens out of your kit, I would bring the 28-80. Just to warn you, you will have to be a fair bit back to get all the fireworks at Magic Kingdom at 28mm, but you'll get good shots
Have fun!