Hello , Welcome to Healthcare Magic forum. According to your description the cough most probably seems to be allergy or asthmatic cough.Though there are other possibilities like viral infections, bacterial pneumonia, bronchiolitis all of which are common causes in young children. Cough syrups are either bronchiodilators, mucolytics or cough suppressants used depending on the type (wet or dry cough) and cause of cough. So first of all the diagnosis has to be confirmed by clinical auscultation, xrays and blood tests (cbc, esr)if needed. Once it is confirmed then appropriate treatment like a course of antibiotics, anti allergic medicines (steroid or antihistamines), and suitable cough medicines may be started . Aerolin is a bronchodilator and useful in case of asthmatic cough but is a temporary relief medication and hence if the cause of cough is not treated then it may persist. So please consult a chest physician or his pediatrician for confirmation of diagnosis and further management. Wishing him a speedy recovery . Regards