Wendy, our family's trip is 1/30-2/6, and we're waiting to tell them Christmas morning. I am sending DS1 (age 10) and DS2 (age 8) on a scavenger hunt... 10 clues hidden around the house, and at the end they will find a large wrapped box. When they open it, Disney helium balloons will float out, with a sign attached that says, "We're going to Disney World in 36 Days!!" I'll have Disney tees, a couple of Disney video games, some trading pins, and a couple of other goodies in there. I'll also have a countdown chain in there as well.
They counted down for over 4 months before our last trip and it was just too long. I can't wait to see their faces when they finally find out we're going back! We were there this February, and they don't expect to go back for another 2 years. I couldn't wait that long!
Have fun, how ever you decide to tell them!!