Insect Bite Reaction: This is the most common cause of severe ear swelling in a child after a bug bite. The reaction can range from mild to severe and is often due to an allergic response to the bite.

Cellulitis: A bacterial infection of the skin that can occur after a bug bite, especially if the bite becomes infected. Symptoms include redness, swelling, warmth, and tenderness.
Allergic Contact Dermatitis: An allergic reaction to substances in the bug's saliva or other environmental allergens, leading to skin inflammation and swelling.
Impetigo: A contagious bacterial skin infection that can start with a bug bite, characterized by red sores, blisters, or crusts.

Mastoiditis: An infection of the mastoid bone in the skull, located behind the ear. It can occur if an ear infection spreads, and symptoms include ear pain, fever, and swelling behind the ear.
Perichondritis: An infection of the cartilage and the tissue surrounding the ear, which can be life-threatening if not treated promptly.
Erythema Multiforme: A skin condition characterized by target-like lesions, which can be triggered by infections or allergic reactions, including those to bug bites.

Kawasaki Disease: A rare condition that mainly affects children under the age of 5, characterized by fever, rash, swelling of hands and feet, and other symptoms. While not directly caused by bug bites, it can be considered in the differential diagnosis of severe swelling and rash in a child.
Angioedema: A rare but potentially life-threatening condition that causes swelling of the deeper layers of the skin, often around the eyes and lips, but can also affect the ears. It can be triggered by allergic reactions, including those to insect bites.