Hi madam, your son has adenoids. Adenoids are lymphoid tissue present behind the nose.they are small at birth but increase in size after 3 years of age. Due to this, childrdn are prone for repeated cold attacks, fever, throat infection, breathing throughmouth, snoring in night. Symptoms will gradually reduce by age of 10, the adenoid size will gradually reduce over time by age of 10 yrs. But until then its hard time. Incase his adenoids become very big compromise ing his airway , then u have to take a xray of adenoid, confirm the size, if its too big then get it operated and removed after the age of 5 years, but upto 5 yrs his mouth breathing will continue. But dont worry every kid has this problem .some kids get over it, but nothing to worry.