Preheat oven to 350 degrees F.
In a large bowl, sift the all-purpose flour, baking soda, baking powder, salt, and set aside.
In a large separate bowl, combine the eggs, milk, sour cream, vegetable oil, and vanilla extract, set aside.
In a standing mixer, mix the butter and sugar until well combined.
Add the flour mixture and the wet ingredients to the butter mixture and mix until well incorporated.
Fold in the rainbow sprinkles.
Using an ice-cream scoop, scoop the batter evenly into your muffin tin and bake for 16-18 minutes.
To make the frosting, mix the butter for about 2 minutes or until smooth.
Add the unsweetened cocoa powder, powdered sugar, vanilla extract, milk, and mix on medium-high speed for about 3-4 minutes or until nice and fluffy. 
Use a piping bag or offset spatula to frost the cooled cupcakes and Enjoy!
