This is what I did. 4 Years ago, my Daughter was 5 and my Son was almost 3. The kids were bugging to go to WDW, but I kept avoiding it by telling them that all the planes were full. Of Course they kept asking. My wife and I booked a trip and decided to keep it from them. I'm a flight Sim freak, so one day I was infront of the computer doing a commercial flight in Flight Silulator 2004, and my Son comes up to me and asks if I'm flying to Disney. I said no, and again he asked. Again I said the usual, that we can't go because all the planes are full and we can't get tickets. I have my computer in the basement, and I hear a box getting dragged behind me. I turn around and ask him what he's doing. He says, with a rather annoyed look on his face "I'm building a plane, so we can go to Walt Disney World" I just about choked.
The night before we left, they spent the night at my parents house. With them, we left some Disney clothes for them to wear the next day.
That night, my wife and I packed all our stuff, and loaded the car. In the morning we met my parents and kids for breakfast. At the end of the meal, I said, "Hey, do you guys want to go down to the airport and watch the planes land" they were all for it. So we hop in the car and head down to the airport, and park in the parking garage, my wife moves the kids up ahead while my dad and I trail out of sight behind with the baggage. We get into the terminal, and when I have them standing infront of the checkin counter, I break it to them. My dad fires up the camcorder, and hits record. So I tell them, "remember how we told you the Plane was full? Well we got tickets and we are leaving for Disney World today"
HOWEVER, I didn't quite get the result I was going for. My daughter starts crying. So I ask her why she's crying, and she says that she doesn't want to go on an airplane. My son's jumping up and down with excitement, and she's balling. Now what? Being in Canada at Toronto's Pearson Int'l Airport, we check in our bags and get into the US Cutoms line to go through, she's still sad, but as soon as we got through and saw the kids in the waiting area, and I showed them the plane, she came around.
Once we rolled down the runway and the wheels lifted off the ground, she was overjoyed. And we had an AMAZING TIME! We went back the next 2 years, and she loves flying now.
Bottom line is, careful how you do it. Not everyone will have the same reaction, and although my idea backfired like an old dodge, it all worked out in the end. GOOD LUCK!