Combine flour and baking soda. Microwave chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted; stir until chocolate is completely melted and mixture is well blended.
Add granulated sugar and vanilla; beat with mixer until blended. Beat in eggs, 1 at a time.
Add flour mixture alternately with water, mixing well after each addition.
Spoon into 12 paper-lined muffin cups.
Bake 19 to 21 min. or until toothpick inserted in centers comes out clean. Cool in pan 10 min.; remove to wire rack. Cool completely.
Tint COOL WHIP with food coloring; spread onto cupcakes.
Cut each marshmallow crosswise into 5 pieces with kitchen shears to resemble flower petals; press cut sides in colored sugar. Arrange 5 petals, sugar sides up, on top of each cupcake to resemble flower; fill center with candy.