How do you treat erythema multiforme in a 1 year old?

Supportive care: You first want to identify & remove any trigger, like a strep infection that can be treated or food that is setting off the reaction. The rest is supportive. Fluids as tolerated or by IV if not. Meds for itching if a problem. Anti inflammatory steroids are standard to calm the reaction, used in treatment doses first & withdrawn as the reaction fades.