My son had been to WDW before but doesn't remember it because he was 1 and 2 on those trips.
He didn't go again until he was 6. Since this was the first trip he would remember we decided to do a big surprise as a way to tell him we were going. His birthday is New Year's Day and we would celebrate it a day or 2 after so that people could come to his party without it interfering with their New Year's plans.
We had all of the party attendees wear something Disney related if they had it. Most people wore Buzz Lightyear, Cars, or Pirates t-shirts since they are all over
Walmart and Target.
I got party supplies from Party City. Mickey napkins, Tigger cups, POTC party favors. I got several helium balloons with various Disney characters on them. There was a Cars pinata.
I didn't ask my son what theme he wanted his birthday party to be, and he never mentioned anything, so I went with the everything Disney theme.
When we were opening presents he opened an envelope that had a big ticket (I made it using my Cricut machine) It kind of looked like the ticket from Polar Express. It was gold but it had Disney character stickers all over it and said "Ticket to WDW" I asked him what do you think WDW means? He instantly guessed Walt Disney World. The next gift he opened was the Guide to the Magic For Kids book. There were a few Disney t-shirts as well. After he opened the Disney gifts he asked, "Is this Disney ticket real?" I said it sure is and we are going tomorrow! He was so excited it was difficult to get him settle down long enough to open the rest of his regular birthday gifts.
That Guide to the Magic For Kids book was one of my best purchases. Two years later he gets it out regularly and flips through the pages reliving all the memories we had on that trip. He points out which ride he liked the most (which changes a lot) and which ones he wants to try next time. Little does he know we're going for Christmas this year. I'm working on plans for that surprise.
I know this is a birthday story, but you could do most of this stuff for Christmas. During the holidays there is a lot of Disney themed wrapping paper for sale.