Draw a face on the bag with markers. Allow to dry over night. Place on top of balloon and paper mache over top to form stem. Sit balloon with stem side up to dry so that the bottom remains partially flat. The next day when dry, paint orange with paint.
Paint stem green.
Once dry, paint in eyes and other details. Flower vines can be purchased at craft stores if you wish. These make nice window ornaments instead of real pumpkins, however, do not use a candle inside. For smaller pumpkins use lunch bags with flat bottoms, for larger pumpkins use grocery bags. Gather top of bag and tie with string or yarn to form stem of pumpkin.