How does 2 years old half child cough to have phlegm to do

Children cough sputum is mostly caused by respiratory tract infection, because the child's immunity is low easy to be infected by pathogenic bacteria, it is suggested that parents usually give the child more water, can dilute sputum to help alleviate cough symptoms, if cough expectoration is more serious, can take the child to see a doctor to check the cause, through atomization inhalation to relieve the child discomfort.