Reactions to foods in children most commonly present in infancy.
Six or seven foods create the majority of reactions including cow milk, egg, peanut, nuts, fish, shellfish and seeds. Milk and egg sensitivity are the most common, probably occuring in 1% of children. Peanut sensitivity is only slightly less common. Foods other than the ones listed above can be sensitizing but less commonly.
when children are allergic to food, it usually occurs in the first two years of life. At age 3 the window for food sensitivity usually closes and the children become allergic to aeroallergens after that. That is called the allergic march. After age 3, it is less likely for children to become sensitized to a food but it is not absolute. After all some adults become sensitized to foods especially nuts, fish and shellfish. A major exception to that generalization is the "Fresh Fruit Syndrome" or "Oropharyngeal Syndrome". This is a reaction to certain raw fruit that is localized to the mouth and throat. It is a cross-reaction between an allergen in Birch pollen and raw fruit. The allergen breaks down when heated and the patient can tolerate the fruit when it has been cooked but not raw.
Children commonly outgrow the sensitivity to cow milk and egg after age 1 close to 18 months of age. If they have not lost the sensitivity by age 2, they will be much slower to lose this sensitivity although they often tolerate tiny amounts of milk or egg in baked goods and are unlikely to have a threatening reaction. It is much harder to outgrow the sensitivity to peanut and nuts although about 10% of children who are not very allergic can lose the positive skin test and a full 20% lose clinical sensitivity even though some of them still have a positive skin test.
Peanut and nut are the foods causing the most threatening reactions, partly because they are strong allergens but also because they are common food stuffs and are found in many different baked goods and confectionaries. Fish, shellfish and seeds can also create significant reactions but can be avoided more easily.
Children with asthma are at more risk from a reaction to a food since they are more likely to target to the chest especially if their asthma is under poor control.