A cough for 3 days in a child is most often due to a simple viral cold and usually improves on its own within a few days, so it's reassuring that the severity has already decreased. You can continue supportive care like giving plenty of warm fluids, steam inhalation (if age-appropriate), and keeping the child well hydrated, while avoiding cold foods and exposure to dust or smoke, and using honey for cough relief if your child is over 1 year old. Medicines like mucolytics or cough syrups often give limited benefit and should not be increased or changed without a doctor's advice, and antibiotics are not needed unless a bacterial infection is suspected. However, you should consult a paediatrician if the cough lasts more than 5-7 days, becomes severe, is associated with fever, fast breathing, wheezing, vomiting, poor feeding, or disturbed sleep, as the doctor may examine your child and decide if any further treatment is required.