HEAT oven to 350ºF.
PREPARE cake batter as directed on package. Pour into 24 paper-lined muffin cups. (Batter will nearly fill cups.) Bake 26 min. or until tops are light golden brown. Cool in pans 10 min.; remove to wire racks. Cool completely.
BEAT cream cheese, sugar and milk in medium bowl with mixer until well blended. Stir in COOL WHIP; spread onto cupcakes.
TOP with berries. Keep refrigerated.