I started with a somewhat flat, taller box for the main part of the house, which is, of course, an amazon box that's being upcycled. I used regular school glue to paste on white printer paper, to give myself a flat surface to draw on, but construction paper would have been more ideal.
Next is to draw on the house, although if you prefer you could cut out shapes from construction paper and glue them on. You could even make this into a project for kids to do for themselves! If I'd thought of this sooner, I would have set up a little station and had the two boys make their own haunted house.
Once the decoration is on the front, I used a box cutter to carefully cut out the door, and windows, so that they will open. I considered gluing on handles of some sort, or poking something through for them have an easier time opening the windows but decided against it. Having them slowed down for a moment won't be terrible.
I taped the treat to a bit of yarn and then taped that inside the window and doors; one treat for each child. I also tapped some 'blank' string on the other openings.