It could be a cold, viral infection, or other causes such as allergies. Therefore, a pediatrician should check your child.

Also, cough with clear to white phlegm is less worrisome. But if cough becomes more persistent and affects sleep, then get it checked out.

It can be. But the most common infection is virus for which treatment of the symptoms is all you can do. It can also be a sign of allergies. If there is high fever or the mucus is thick and colored, you may be getting a secondary bacterial infection that may need antibiotics