Prepare the cake mix as directed on box and allow to cool completely.
Whisk together instant pudding, milk and powder sugar in a large mixing bowl for approximately 2 minutes.
Stir in the Cool Whip to the pudding mixture.
If the mixture seems to be a little runny, place in the refrigerator for a few minutes to firm up.
Spread on cake or cupcakes.
Enjoy!
Notes
If you have any remaining frosting (which you wont because the kids will quickly lick the bowl clean), it can be stored in the refrigerator of a day or so.