The first-line treatment for cough related to an upper respiratory tract infection (URI) in a 4-year-old child is:

Dextromethorphan and guaifenesin syrup (Robitussin DM for Kids)

Fluids and symptomatic care

Guaifenesin and codeine syrup (Tussin AC)

Chlorpheniramine and dextromethorphan syrup (Nyquil for Kids)