The herpes in the mouth of a child with fever is usually due to hand, foot and mouth or herpetic pharyngitis and other conditions. 1. hand, foot and mouth: children fever mouth herpes may be caused by hand, foot and mouth disease, hand, foot and mouth disease is mainly due to viral infections, usually through the digestive tract, respiratory tract or contact transmission, usually the patient will be manifested as a sore mouth, anorexia, low-grade fever, hands, feet, mouth and other parts of the appearance of small herpes and other symptoms. 2. Herpetic pharyngitis: Herpetic pharyngitis may also lead to children with fever and herpes in the mouth, usually the patient will have fever, sore throat, small herpes in the mouth, soft palate and tonsils, palate, and so on. Children’s fever mouth blisters may also have other causes, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.