We made a calendar from one of the blank ones at the school supply store. Each day of the month had a post-it with the date on it; under each day I had a Mickey head shape with the number of days remaining until we left. Each morning we'd pull off the date and see how many days left. Many of the days I had trivia questions listed or "look here..." for a treat kind of thing. The week before we left each day revealed where in WDW we'd be the next week on that day.
Not sure what I'm going to do this time as we are telling them earlier we did for our last 2 trips- 9 months out instead of 1!!! Sorry the pic is so big- I tried to reduce the image size, but was having trouble.