First off, go to a specialist who specializes in children's allergies. They will probably run what is called a "RAST" test, this is a blood test that is taken for many types of allergies, both food and environmental. It usually involves a few vials of blood, but that is all.
Hello, and yes I have a 6 year old daughter with multiple allergies. They do a blood test sometimes and others they do a number cart in their backs. The write 1-43 on their backs and stick them with 43 different things they could possibly be allergic to. The pins sort of look like thumb tacks. The kid will probably be terrified but they mostly don't feel the pricks but if they are allergic to any of it, it will itch like crazy.
I meant on their backs, sorry.
Oh and my daughter also have asthma pretty bad. Her allergies are peanuts, tree nuts (like walnuts and so on), sesame seeds, lima beans, weeds, trees and grass. I hope this helps. She was just retested last week.