LOL, the one time we decided to completely surprise DS it was a bust in a lot of ways. No, nothing really bad happened, but it got the trip off to a difficult start.
He was 5 at the time. He had a few days off school, so we planned a surprise trip to start right after school let out on the day before the break. Dad picked him up and told him that there was a surprise waiting for him at home. We had everything packed up and waiting in the kitchen with a big sign that said We are going to WDW -- RIGHT NOW!! He gets home, sees the sign, looks at Dad and says, "Where's the surprise?" In his 5 yo mind, a surprise had to be a thing, and there was no new thing there, so he didn't get it. However, he's game for any trip, so off to the airport we went.
The plane was delayed a bit, but as we landed at about 10 pm, and he heard the pilot say "Welcome to Orlando" - he looked at us and suddenly, the reality hit -- Orlando is in Florida. At that point, he was still a tiny bit suspicious, but when we drove under the arch, he realized that it was all completely true, and suddenly he started bouncing off the walls with excitement. The problem was, at that point it was about 11:30 pm, and both of us were exhausted from the trip after working all day. No amount of coaxing or threats were going to get him to go to sleep. Finally we just locked the doors and put the Disney Channel on low volume, and we went to sleep though he didn't finally conk out until around 3 am. (DH is a light sleeper, and was waking up often.)
The entire first day of the trip we were all zombies.