How does 4 months half moon darling cough to have phlegm to do

The baby has cough and sputum, which may be the cause of upper respiratory tract infection. Please feed warm boiled water to help dilute the sputum. If the cough and sputum symptoms cannot be relieved, it is necessary to see a doctor in time for treatment. Check the blood routine and chest radiograph. If the sputum is difficult to discharge, aerosol inhalation can be used for treatment.