Follow directions on box for cupcakes.
After baking move to cooling rack.
Combine butter and marshmallow cream in medium bowl on medium speed until blended.
Slowly add sugar beating until well blended.
Gradually add milk until desired consistency is reached.
Transfer half of icing to another bowl and add green food coloring and mix well to blend color.
Transfer green icing to zippered bag and clip corner to pipe.
Cut a small square in the center of each cupcake.
Fill hole with green icing.
Cut off inner part of removed "plug" and replace in cupcake.
Ice top of cupcake with white icing.
Place Lucky Charms pieces on top and sprinkle with green decoration sugar.