Food allergies in children can manifest subtly with symptoms like stomach pain, rashes, and runny noses, often mistaken for common childhood ailments. These reactions occur when a child's immune system identifies harmless food proteins as threats, typically appearing within two hours of consumption. The 'Big 9' allergy-causing foods include milk, eggs, peanuts, tree nuts, soy, wheat, fish, shellfish, and sesame. While milk and egg allergies are often outgrown, peanut and shellfish allergies tend to persist and can cause severe reactions.