This may be a bit long winded, but I'm rather fond of the "reveal", and when I'm fond of something, I tend to ramble, so apologies in advance...
The first year, I didn't tell her squat. She was 5 at the time, and I flew up to DC to pick her up. She thought she was flying back to Atlanta to spend a few weeks with me. I made sure to book a window seat for her (as I always do) and as we were landing, she made the comment (which I thought very observant for a 5 year old) that "Atlanta doesn't have this many pools and lakes.") I continued to play dumb.
A bit of back story, it was my first trip back to Disney in many, many years, and my first trip as a parent. My theory was that she wouldn't figure it out until we got to the TTC and I'd get the big "reveal" when we got to TTC and boarded the Ferry and she first saw the Castle.
Boy, was I wrong.
We got off the airport, and she obviously couldn't tell the difference between MCO and ATL (there is a HUGE difference)...and she griped about how heavy her bag was to pull (it wasn't heavy, most of her clothes were packed in my bag, her bag consisted of mostly stuffed animals, her favorite blanket, and toys, but...she was 5...)
We made it all the way to the sign, and she saw the logo sign they used in 2010 for the Magical Express, and froze and squeaked out...
"Disney...DISNEY! THE MAGIC CASTLE!"...I don't know the exact words outside of fading memories, but it was sheer excitement, and I certainly didn't have my camera ready! Then she noticed the busses and started to ask me if we could go. I continued to play dumb (figuring I could drag it out)...and told her to ask the attendant who checks your ME tickets if we could go.
The CM had caught on, and played along. She said "Only if you have tickets", which of course resulted in a query from the kid, and I pulled out the ME tickets and said "ask her if these will work". Of course they did, and our trip was on.
In 2011, having learned my lesson from the year before, I had the camera out. She again noted that something wasn't right, but didn't connect the dots, and didn't recognize MCO.
She thought we had flown to DC, because I said "We are going to meet Mommy." Technically we were...so I didn't lie! (her mother joined us later in the trip).
But, THIS time I had my camera ready!
Skip to 1 minute in to see the "reveal"...
Oh, and as a side note, her mother and I were trying to work on her "whining" at the time, and we used the "We are the Knights" joke to chide her in a playful manner (at other times she got actual lectures on it)...seems to have worked, because she doesn't do it now, but as any parent knows, this is a phase.
Anyhow, when she screams "Mickey Mouse!" is one of my favorite things to see, she realized EXACTLY where we were, and what was coming.
So, fast forward to trip 3, in 2012. For this trip, I told her in advance (about 2 weeks in advance) thinking that we would plan out the trip together. However, while she was excited, it wasn't the same. Since she knew, there was no reveal when we got there, and at 7, she wasn't ready to really start planning anything. I jumped the gun. It didn't sully the trip for either one of us, but I only have a few more years left where I get to see her so physically and emotionally excited about the Mouse in that way. My little girl is growing up...
This year she is 8, and her mother and I have kept the trip a huge secret from her (even when she had to go get a Passport)...we'll see what happens.
I think...keeping it a secret, or misrepresenting...is the way to go.
My opine.