Preheat oven to 350°F. Line 36 mini cupcake pans with paper or foil liners. Prepare cake mix according to package directions, but substitute buttermilk for water and use four eggs. Spoon batter into prepared cupcake pans. Bake until a toothpick inserted into center comes out clean, 15 to 20 minutes. Transfer to a wire rack and let cool.
Frost half of cupcakes with vanilla frosting and half with strawberry. Roll cupcake edges in sprinkles. Spoon chocolate frosting into a resealable bag and snip the corner. Pipe letters and place candies on cupcakes as shown.