The answer? You don't! Instead, you use mis-direction, like any good magician would!
We were able to keep a two week trip a total surprise from DD when she was 6. That was easy; just plan, wake her up on the day and head to the airport.
This time around presents a totally different challenge. DD11 knows all the travel videos and specials that TIVO routinely captures, knows where every file on the computer is (I have no idea how we used to plan WDW trips before the internet...), and routinely is the first to see the mail when it comes in for the day. So, we knew right away that surprising her was completely out of the question.
So when she woke up this morning (Sunday), she looked at me and said "five day dance until we leave on Friday!". Cool! She still doesn't know that we switched airlines, and are leaving a day earlier on Thursday. Hopefully, she won't know until SIL shows up at the door Thursday after school to drive us to the airport. We're having SIL inform DD that she needs to gather her last things so that we can leave right there and then.
Once we get to MCO Orlando late Thursday night, she's riding shotgun in the front seat and acting as navigator from the airport to WDW. She's convinced we're staying at PO-Riverside for the entire sixteen days (she thinks it's fifteen). And she should be....we told her to hold on to the reservation that Disney sent us when we made that specific reservation, and that she'll get to present it to the front desk when we "check-in" at POR. She doesn't know that it's been cancelled.
As we're driving to WDW from the airport, she knows that it's her job to be navigator, and watch the signs to take us first to WDW and then to POR. I'm planning to ignore her last directions and continue straight to WL, where we're spending the first 6 nights. If we know our DD11 well, she'll get upset with me when I challenge her that she misread the signs because "We've been there before, and I'm going the right way to the hotel". She'll be confident (and correct) that I missed it, and firm in her belief that I should turn around. I plan on having a mock argument with her, all the while driving on to WL. I plan on telling her that we're lost, and that I'm pulling into the gate at WL to ask directions, at which point we'll tell the guard that we're here to check in. DW will be ready with the camera in the back seat to take pictures of her when she realizes that she's been had......again!!!
Sooooo, four days to go, and we're still trying to figure out how to tell her she's also getting 5 days at the beach club (she's always wanted to go to Stormalong Bay in the worst way), and then ending with 5 days in one of the newly renovated rooms at the Contemporary on the tenth floor. Any sneaky folks out there have any ideas?
I've had fun reading about all of your plans, so forgive the longwindedness, but I had to share mine as well!