Fever in children should not exceed 3 days at most. If it exceeds 3 days, the condition may progress and become complicated, but it needs to be analyzed on a case-by-case basis and cannot be generalized. There are many causes of fever in children, but if it is caused by the common cold, most of them can subside within 3 days. If it is the flu, the fever may last for 1 week, and if it is an infectious disease or pneumonia, the fever may last for 7-10 days. If the fever lasts for more than 3 days, a combination of bacterial or mycoplasma infections should be considered and treated with antibiotics under medical supervision, and the fever usually does not last longer than 3 days. If antibiotic treatment is not effective and the fever again exceeds 3 days, EBV infection or an immune disease such as Kawasaki disease should be considered. If the fever persists for more than 5 days and the symptoms are not relieved, along with rash and worsening cough, prompt medical attention should be sought. In addition, children’s resistance is weak, so if the fever lasts for more than 3 days, it is recommended to promptly visit the pediatric department of the hospital to check the specific cause of the fever and treat it under the guidance of a doctor.