Place cereal in a large bowl coated with cooking spray; set aside. Melt butter in a medium saucepan over medium heat and add marshmallows. Stir until smooth. Pour over cereal and stir to combine. Spread out in prepared pan and press firmly to flatten. Let stand until cool, about 1 hour. Trim edges and cut into 30 3-by-1-1/4-inch bars. Push a popsicle stick through one narrow end of each bar.
Using an offset spatula, spread a thin layer of white chocolate over tops of 15 bars. Repeat, using semisweet chocolate for remaining 15 bars. Transfer to a baking sheet and refrigerate until set, about 20 minutes. Place a wire rack over another baking sheet. Dip the white bars in white chocolate and the semisweet bars in semisweet chocolate; place on rack, allowing excess chocolate to drip off bars. Refrigerate until firm, about 20 minutes. Makes 30 pops.
To paint faces on bars: