I just found out my baby has a dairy allergy.

What does everyone do when you have to make butter free Butter Cream frosting?!?

try searching for Vegan Buttercream...

You can use a shortening-based or margarine-based icing.

You can use an all shortening recipe my recomendation so the icing is not to oil tasting to use high ratio shortening for that smooth taste

Here's the recipe I use for what I call decorators icing
2 cups crisco
4 tablespoons water
2 teaspoons of your favorite flavoring (butter, vanilla, almond, lemon etc)
mix then add slowly 2 pounds of powdered sugar you may need to add more water as you go
You can replace to taste the water with the flavored non-dairy coffee creamers
Hope this helps!

Jibbies

Here is my favorite recipe...

2 lbs powdered sugar
1/2 c. liquids
(in the half cup measuring cup I put 1-1/2 tsp. vanilla and the rest water)
1-1/2 c. all shortning crisco (I use the generic all shortning)

Mix well.

http://forum.cakecentral.com/buttercream-with-earth-balance-ftopicp-359073.html#359073
in case you don't do the 100% shortening icing...