Spray 13x9-inch pan with nonstick cooking spray. Melt butter in Dutch oven or large saucepan over medium-low heat. Add marshmallows; cook about 3 minutes or until melted, stirring constantly. Stir in vanilla. Remove from heat.
Add cereal; mix well. Stir in gummi bear candies. With sprayed fingers, press mixture in pan. Cool 30 minutes or until completely cooled. Cut into bars or into shapes with cookie cutters.