Coach Rick ~ we surprised our kids with a
Disney Cruise this past January. It was so much fun to surprise them, but a lot of work!! DH slipped up a couple of times but thankfully DD's did not catch on.
We told them DH had to take a business trip to FL and we were going to tag along and hang out at the hotel and swim, go to the beach etc. Dh travels a lot for work so they never questioned it. At the time that we booked that trip, the passport laws said you needed passports to cruise starting Jan 2007 so I had to get the passports "just in case" we wanted to travel out of the country. DD9 questioned it a couple of times, but I just kept telling her it will be good to have for when we decide to go on a cruise again "in a few years"

Of course, then they changed to passport requirements but at least we have them now.
I made t-shirts with a cool graphic of the ship and
Castaway Cay and wrote on it "our SURPRISE Disney Cruise" The day after we arrived in FL, I laid the clothes out on the beds and told DD's to get dressed so we could go to breakfast. We arrived very late the night before so they girls were still half asleep, so they didn't really get it right away. I kept saying "what do you think of your new t-shirt" and DD9 said "oh it's cute!" but she didn't get what it was saying!!
Finally DH said "do you guys want to go swimming" and since that's their favorite thing to do, they said yes. He said "how about if we go to the Mickey pool today" and they were like "uhmm, Dad, that's only on the Disney ship" He said, "okay then I guess we'll have to get on the ship today" and it finally sunk in
I had to be sneaky about the pirate stuff too, I just packed it at the bottom of the suitcase that had DH and my stuff in it. I figured they would never look in there. For the formal clothes, I had told them the "hotel" we were staying at had a really fancy restaurant and they would need to dress up for it. They bought it hook, line and sinker! Not really a fib, I mean the ship is really like a big floating hotel right??
Good luck with pulling this off ~ it was so much fun!!!