it may seem extreme, but i highly recommend finding a city and finding someone who is an experienced traditional chinese medicine doctor or an ayurvedic doctor.
both of these traditional forms of medicine have ways of managing food allergies--even curing them in some or many cases. often, it requires a trip to china or india. but, i know it works.
one of my aquaintances had a son who was allergic to everything. He was allergic to nuts, eggs, dairy, soy, gluten, many fruits (mostly berries) and vegetables. he could manage rice, small amounts of breast milk, and a few fruits and veggies (which his mom steamed and pureed into baby food--you can make your own baby food).
She took him to an ayurvedic doctor who was visiting from india. she heard about the doctor through an indian woman in her yoga class. my acquaintance was talking to another student in the class about her son's allergies and how he was now loosing weight and showing signs of malnutrition. the woman overhead and recommended that she make an appointment with the visiting doctor.
in ayurvedic medicine, allergies are not issues of the immune system (though that's where the symptoms come from), but rather issues of the ability to assimilate nutrients from certain sources. Thus, the solution is to reset the body so that it can assimilate, rather than avoiding foods and fighting the immune response.
when my acquaintance took her son, the doctor gave him a good examination and history. he then recommended that she come to india--to his clinic and hospital where he could treat her son because everything needed was more readily available there. She made arrangements to take her kid to india for the 6 weeks that the doctor recommended. The doctor also noted that she had assimilation issues and wanted to treat her as well.
She arrived in india very nervous, but willing to try anything because of her sons increasingly failing health. she said that the first three days were the hardest because both she and her son only consumed clean water at room temperature and specialized herbal teas at room temperature. They also had specialized massage sessions (with special techniques, oils, and herbs), plenty of rest, and yoga (since her son was under 3, it was fully assisted yoga, more like thai yoga massage).
Then, on the third day, both she and her son were given herbal supplements (she doesn't know what) and food was reintroduced. Raw (unpasturized), fresh organic milk was given--and her son had no reaction. Then, they introduced vegetables, then fruits, then legumes, then nuts and seeds, and then grains. Each item was introduced after a few days. So it was a few days of just raw milk (room temp), then after a few day, raw milk with vegetables. then raw milk with vegetables and fruits. you get the idea? foods were introduced systematicly because according to ayurveda, allergies are caused when the body is not prepared to accept a certain food--and yet we introduce it anyway. Most kids in the west are given grains first (milk, then grains) before anything else in the form of cereals. But in ayurveda, these should be given last, and they should be given in a sprouted, soaked (buttermilk or lacto-fermented) forms rather than the processing that we do in the west. The regimen of massages and yoga also continued.
When she left india and returned to the US, her son had NO food allergies. if she keeps him sugar free (no white sugar) and on whole, natural foods (they're omnivorous, but he's lacto-vegetarian using ayurvedic principles), he has no reactions. when chemicals are added--processed foods and such--he begins to have reactions to those elements and develop intolerances toward 'normal' foods.
I believe that it is possible to 'cure' kids of food allergies with the right process. i believe that a traditional chinese medical doctor or an ayurvedic doctor can help parents do this.
but, it takes a lot of work and a lot of money.