The Epsom Salts helps to pull out toxins and the baking soda will soothe the skin. I don't know how long it will take to heal the skin.
A good cream to use would be a baby bum cream with zinc oxide as the base of the cream. This is also an antibacterial cream but in a more natural way. Penaten cream has zinc oxide.
In a small baby bath i would use 1 tablespoon Epsom Salts and no more than 2 tablespoons of baking soda.