I make my own icing.
I take 1-2 tablespoons softened butter and pour some powdered sugar into a bowl (amount depends on the amount of cookies you make. I often double or triple this recipe as we give a lot away.) I combine the butter and sugar and then add some milk. I add just a little bit of milk and keep adding a little bit until I get the consistency desired. You want it rather thick so it does not drip. I also add a little vanilla. I then divide the frosting into different bowls and color it whatever colors we need. We ice the cookies and put sprinkles/candies on while the icing is still wet. Let frosting dry before stacking for storage. I usually put wax paper between layers. You can freeze the cookies with or without the icing.