Heidi,
OK, let's take this in two parts. In the next reply I will lay out what parks on what days. But for now let's chat about the Polynesian and how to break the news to them!
I adore the Polynesian resort. Of all the wonderfully themed Disney resorts, it is the one where I feel the most transported to a different place. You can use that. Perhaps on your flight you have the family dress like they are going to a luau? Or at least have some inexpensive leis ready for when they get off the plane? You could even use the theme as a series of pre-trip hints to see who can guess their destination.
For your time at the hotel, make sure to enjoy some of the resort specific fun. Explore the grounds, enjoy the pools, and soak in some of the polynesian culture. There are lots of events throughout the day that showcase island culture, but I like just to visit the area to the left of the lobby as you enter the resort's main longhouse. There you typically have a cast member on duty who is from a polynesian island who will tell children about their home culture, including working on some crafts at times.
OK, that is it for now. Check my next answer for your park plan!
Have a magical vacation!