I would never advise you to give asthalin cough
syrup to a child of 3yrs untill unless the child has severe breathing problem,a symptom of asthama.You have not mentioned the severity of cough or the respiratory trouble your child has.Anyways,in my opinion,give the child any cough syrups like,tixylixs or even benadryl
syrup in case of cough.severe cough,you can give her steam(plain water....NO VICKS
VAPOUR),or nebulise her with normal saline and salsol,this help in relieving the symptom remarkably.
But mind you,if the child is excessively breathless then go ahead with asthalin expectorant without much thought.just give a reduced dose.............Or else...you surely can avoid it.....take care.