I used to make gingerbread houses this way with my young preschool children.
You can use different types of cookies for the roof, windows, and siding. Buy a variety of graham crackers and small cookies at the local market. If you don't have small juice or milk cartons, use a small box (covered with foil) or even a round margarine tub-(use round cookies for the siding.)
Licorice whips, twists and rectangles cover up the cracks. Also, bulk hard candies, chocolate chips, nuts, gumdrops and lollipops make the house look good enough to eat.