After removing the problem foods you do have to make sure your child is getting the proper nutrition (including supplements), enzymes, and possibly consider something like a rotation diet. Unfortunately eliminating those foods is not the only thing you need to do.

Enzymes are important. The right nutritional supplements can lessen the allergic effects or even eliminate them altogether. The most important nutrients are vitamin b6, zinc and vitamin c.

Have you consider a rotation diet? This is a big challenge as it requires some advanced planning, but it does allow for more variety.

http://www.food-allergy.org/page2.html