I think I would come home from work, eat dinner, act like it was a normal night, until I got my suitcase out. I would start filling it and wait for them to ask...then say...well I am going to Disney World tomorrow to celebrate your birthdays...and see what happens.
As I was reading this I imagined my DW doing something just like it if she were to ever surprise us with a trip.
Only my DW can be a prankster at times so I imagine she would put a devious spin on it. She would probably start a fake argument about the littlest and most silly thing she could think of. It would probably go something like this:
Me: minding my own business loading the dishwasher after dinner.
Her: "What are you doing?!?! I've told you a hundred times, you can't put nonstick pans in the dishwasher!"
(DW leaves room and returns moments later carrying a suitcase)
Me: "What's with the suitcase?"
Her: "I can't do this anymore."
Me: "What do you mean 'this'?"
Her: "THIS! I can't do this anymore. I'm leaving!"
(Long awkward silence as I scratch my head and wonder what the hell just happened in the last 2 minutes)
Her: "I'm leaving............and you and the kids are coming with me............to Disney World!!!! Surprise!!!!"