Final answer:
The most serious common allergy in children is peanut allergy, which can cause severe reactions including anaphylaxis.
Step-by-step explanation:
The most serious common allergy among children is peanut allergy. Food allergies like peanut allergy occur when the immune system mistakenly reacts to a food protein. Peanuts can be eaten safely by most people but can provoke severe allergic reactions in sensitive individuals. The symptoms for food allergies can range from mild reactions, such as itching and swelling, to more serious conditions like anaphylaxis, which can be life-threatening if not treated promptly.