My parents very generously brought us all on a Disney cruise last summer. My kids (8 and 10 at the time) didn't have the reaction my parents wanted when they told them six months out. My kids really didn't know what a cruise was, and the ten-year-old couldn't understand why it would be so amazing to be on a boat for five days. They weren't pills about it or anything, they just weren't jumping up and down, you know?
But then, I'm a person who needs time to process and doesn't love surprises, so I totally understand why my kids would react that way. We ended up having a fabulous trip, and NOW my kids would have the appropriate reaction!
Best of luck.