Step 1
Preheat the oven to 350°F. Line 24 cupcake cups with paper liners. Prepare the cake mix according to package directions and divide the batter evenly between the prepared cupcake pans. Bake until golden and a toothpick inserted in the centers comes out clean, about 18 to 21 minutes. Transfer to a wire rack and cool for 5 minutes. Invert the cupcakes and cool completely.
Step 2
Print the ABC Cupcake template and cut out the letters. Cut the wax paper into 3- by 4-inch pieces and have several sheet pans handy.
Step 3
Melt the white-chocolate chips in the microwave, stirring occasionally, until just melted, about 1 minute. Place a template on a sheet pan with a piece of wax paper on top. Spoon the melted chocolate into a resealable bag, snip off a very small corner of the bag and pipe the outlines of the letters onto the wax paper. Fill in the outlines with chocolate and tap the pans lightly to smooth the tops. While the letters are still wet, cover them with sanding sugar. Refrigerate until set, about 3 minutes.
Step 4
When the letters are firm, remove excess sugar and peel them from the wax paper; set aside. (Letters can be made up to two days in advance and stored in a cool place.)
Step 5
Spoon 1/4 cup of the vanilla frosting into a resealable bag. Cut the marshmallows in half crosswise and attach a chocolate candy on each cut side. (They will stick.) Cover the tops of the cupcakes with the remaining frosting. Place a letter on the center of each cupcake top. Snip a small corner from the frosting bag and pipe two dots at the top of each letter. Place a marshmallow half on each dot. Pipe a small dot of frosting on top of each of the chocolate candies for pupils.
