We had a party for several of our homeschool friends on the Thursday before Christmas. Here are the results from my kids' efforts. If you click through to flickr, there are close-ups of the other two houses. Click on the photo title "House with conduit" here below the picture, and then click on Candlestring's Photostream to the right of the picture and you will see a few other nice shots.
The small trees and snowmen are marshmallows, and the larger trees are made with buttercream frosting over an inverted sugarcone ice cream cone. Those are fun and easiest for the littlest ones to make (and eat).