I don't have kids myself but in our family telling the little ones about trips always depends on the kids.
My Aunt and Uncle don't tell their kids because they are 6 and under (all the way to 1) and the kids love just hoping in the car and driving for hours so they would freak out with joy if all those hours meant Disney World.
On the opposite side my DBF's niece and nephew are told about everything because at 9 and 11 they have crazy busy schedules and get very upset if they aren't involved. If they weren't told what was up they wouldn't understand why they would have to miss karate, miss parties, miss social dates, etc. These two kids have busier social lives than I do and if they aren't well informed will just pout and be mad the entire trip about what they are missing instead of what we are doing.