Melt margarine in large microwave safe bowl. Add marshmallows, and heat again in microwave until soft and fluffy. Put in a few drops of food coloring to achieve desired color. Stir in cereal and mix well. Using lightly greased hands, shape into small handful sized balls. Place onto pan lined with parchment paper and put candy piece in the top for a stem. Pumpkins aren't generally perfectly round, so it makes this a very kid friendly recipe.