When you put a big smile on the face of your haunted house, you're sure to do the same for your trick-or-treaters.
Measure the inside of an appropriate window and cut corrugated cardboard to fit tightly. Draw a face on the cardboard, then cut out the pieces with a craft knife (a parent's job).
On the interior side of the cardboard, use a glue stick to cover the openings with orange tissue paper.
Set the cardboard in the window and use painter's or masking tape to hold it in place. Place a lamp near the window to light your house-o'-lantern.