Will Steroids Intake Reduce The Child's Immunity?

My son is 3 years old. He often gets cough and cold with the change in the climate doctor says he is allergic to such change he has been advised to take montair 4 also has been prescribed mucolite and deriphylin. with all these medicines for a week he is still wizing hence doctor has prescribed nebulization using beudosal and omnacortil 10 mg twice for three days along with the above said syrups. Shall I go ahead with the priscription. I'm worried to use steroid as my child often falls ill. Will his immunity be effected . Plz suggest.