Don't be a doctor at home unless you have figured out that the food that causes allergy in your child. You may want to go through the link to understand the problem better. https://www.foodallergy.org/diagnosis-and-testing http://kidshealth.org/en/parents/allergy-tests.html http://kidshealth.org/en/parents/allergy-tests.html http://www.webmd.com/allergies/guide/food-allergy-testing
yes they do have. skin test or by blood test, ask your childs pedia
Go to a PD. They can advise you better