Spray two 8 or 9-inch round cake pans with nonstick cooking spray. Melt margarine in large saucepan over medium heat. Add marshmallows; cook and stir until melted. Remove from heat. Add cereal; stir until well coated. Divide mixture evenly into sprayed pans; press firmly with buttered rubber scraper. Cool 20 minutes.
Turn cereal rounds out of pans; cut each round into 12 wedges. Use fingers to round curved end slightly to resemble carrot.
Place frosting in microwave-safe measuring cup with pouring spout. Microwave on HIGH for 30 to 40 seconds or until pourable. DO NOT BOIL. Add red and yellow food color 1 drop at a time, mixing until frosting is of desired orange color. Pour frosting over carrot shapes, covering tops completely and allowing some to drizzle down sides. Reheat frosting as necessary to keep it pourable.
On sugared surface, flatten gumdrop leaves with rolling pin until 1/4 inch thick. With knife or scissors, cut each leaf into 6 strips, keeping them attached at bottom. Place leaf at top of each carrot.