Here is the recipe I used for the tiny cupcakes (per Heather's request). I found the recipe here. It is supposedly similar to the Sprinkles Cupcakes frosting recipe. I eliminated the salt because I used salted butter and found it too salty for my taste.
1 cup butter, softened
3 1/2 cups powdered sugar
1 t. milk
1 t. vanilla
1/8 t. salt
Mix the butter and sugar until blended (I let mine mix in my KitchenAid until they were completely combined and almost "fluffy").
Add the milk, vanilla and salt and beat for an additional 3 to 5 minutes.
I frosted my cupcakes using a Wilton Cupcake Decorator kit. I bought mine at Target, but couldn't find it anywhere online - not even a picture. It is similar to the Wilton Dessert Decorator Pro - but plastic. I thought it worked well and made it easy to pipe the thick swirls of frosting.