Line an 8 x 8 pan with parchment paper, leaving a little overhang on all sides. Prep all of the ingredients in advance, including sifting the sugar and cocoa powder.
Combine the sugar and corn syrup in a medium sauce pan and stir constantly over low heat until the sugar is dissolved. You'll know it's dissolved when the mixture is smooth and easy to stir and no longer feels grainy.
Remove the sugar mixture from the heat and mix in the peanut butter and marshmallow creme.
Then gently stir in the Cheerios. Press the "batter" evenly on the bottom of the prepared pan. Work quickly, before the bars begin to harden.
In a small sauce pan, mix the butter and brown sugar until the butter is melted and the mixture is smooth.
Remove the brown sugar mixture from the heat and stir in the vanilla and milk. Whisk in the powdered sugar and cocoa powder until smooth.
Spread the frosting evenly across the top of the peanut butter mixture, and top with sprinkles. Again, work quickly, before the frosting sets.
Chill in the refrigerator for at least one hour before cutting into bars. Tightly cover and store in the refrigerator. Enjoy!