In a large mixing bowl, cream butter with sugar and egg. Add vanilla and milk.
Slowly mix in salt, baking soda, oatmeal and flour until dough forms.
Take a large chunk of dough and place on a floured surface. Roll out to about 1/2" thick. Press cookie cutters into dough to create shapes. Using a thin spatula, lift the shapes and place onto an ungreased cookie sheet. You can put them close together, they don't expand much at all. Bake at 350˚ for 7-8 minutes (they should not brown at all). Remove cookies from pan with thin spatula and move to a wire rack to cool.
Cream together ingredients for frosting and put about 1/8-cups of frosting into separate bowls. Add food coloring to achieve desired colors. Using a flat knife, small spatula or piping bag with special tips frost cookies. Before frosting hardens, decorate cookies with mini chocolate chips, sprinkles, candy cane crunch or anything else that looks and tastes lovely!