Combine the vanilla frosting and 2 cups of the powdered sugar in a large bowl.
Mix them together using a hand held or stand mixer. When combined, gradually add the rest of the sugar to the mixture, 1/4 cup at a time. Feel the dough periodically to see if it is still sticky. Keep adding sugar until it no longer feels sticky to the touch.
Take the dough out and mix in the sprinkles by hand, kneading the play dough until the sprinkles are fully incorporated. Sprinkle a little at a time until all the sprinkles are used.