Hi, my son is 4 years old and is having cold for last one week. Today, he has also developed cough (specially while he's asleep) and unable to bring out the phelm. Please advise what syrup I can give him.
I also have kofarest-pd at home prescribed by doctor last time he had cough.

Why are you not using he cough medicine prescribed by the doctor if you have some left ?

The more important question is why did you have some left? Those are meant to be used completely unless directed.

Any over the counter children's cough/cold/flu medicine will work. Pay attention to the dosage and the side effects.