A 4-month-old baby with a fever of 39 degrees is a case of high fever and needs immediate heat treatment. you can give oral ibuprofen suspension, which can usually be repeated after 4-6 hours. no more than 4 times a day, according to the weight and according to the dosage on the instructions. If there are symptoms of nasal congestion, runny nose and sore throat, it is an upper respiratory tract infection and the child needs to be given oral busulfan anti-inflammatory oral solution. If there is abdominal pain and diarrhea, you need to get a routine stool check to determine if it is bacterial enteritis. If it is bacterial enteritis, you need to take antibiotics for treatment. If there are no above symptoms, it is better to go to the hospital for a comprehensive examination. In addition, children who are not in good spirits should also go to the hospital immediately.