About your son, I feel he may have an allergic cough, especially if he coughs more at night, associated with vigorous exercise, crying, laughing, or the cough is associated with vomiting. You could try an Inhaler of Foracort 100- Two puffs twice a day, given with a spacer device during his coughing days for 7-10 days. Chocolates in excess are not to be encouraged either in school or at home. Please talk to his teacher about this. His problem is probably genetic, when you tell me about his family background. He probably shall not respond to Homeopathic or Ayurvedic treatment, but his problem shall probably become milder or disappear as he grows older. Do not despair.