For our cruise last year, we left WDW and told the kids we were, "Going to go look at the ocean since we're this close." We happened to find the ocean near the port, where I promptly announced that I needed to use the bathroom....maybe Disney would let me use theirs since I still had my t-shirt & ears on from WDW. As we sat on the drawbridge near the terminal, I flipped down my windshield visor, and a note from Tinkerbelle fell saying, "You are going on a
Disney Cruise" with the date. The kids were in shock all the way through the check-in process, picture with Minnie & walk through the ear tube. The blank look last through lunch, and the giggles started at the Mickey pool.
While they were swimming (DH supervising) I went down to the room to unpack quickly. I wasn't gone long enough for them to notice. When we went to the room after swimming/for muster drill, they found their clothes (princess dresses, priate costumes, etc.) in the closet and it was at that moment that it sunk in that we were really going to be going on the cruise.
We're going to do our best to keep this cruise under wraps for a while. As much as I'd love to show up at the port, I think it will be more important to have the kids make some DIS friends and learn a little about the geography, cruise ports, etc. prior to getting on the ship this time. Still, if you can pull this off as a surprise, it's worth it for that big WOW.