Hi E.,
My son had/had a milk protein allergy too. When he had is blood tested as a baby, it showed he was extremely allergic. They told us to wait until age one to try him on regular milk because babies/kids tend to outgrow it. They also said the less exposure he has to milk, the better chance he has to outgrow it. I stuck to no milk until he was one. At one years old, we tried the milk and he broke out in hives and threw up as he did when he was a baby. Anyway, since then and since it is not life threatening, there have been occasions when he has had some things with a little bit of milk in it, and cake has been one of them. He has not had even a single hive or upset stomach from it. There are alot of other things with a little bit of milk in it that he has had also that he shows no signs of allergy to. They told us to try again when he is 3 (he is 2 1/2). It has been months since I have even seen 1 hive on him, so I think he may have grown out of it, but who wants to test and see their child sick if not. Anyway, I am not sure the extent of your son's allergy, but I just thought I'd let you know in case you thought by 1 years old he may be growing out of it and want to try regular cake. I usually just take the frosting off.