Many coughs are caused by postnasal drip from a cold rather than an actual lung infection such as pneumonia. So how do you know the difference? In general, if your child has a runny nose and is acting well between bouts of coughing, you may be able to just keep an eye on him at home. Although a cough can sometimes linger for a few weeks, it shouldn’t be getting any worse after 4 or 5 days. If your child starts to have fast breathing, the cough isn’t beginning to improve after a week or is worsening, or a fever appears, be sure to have your doctor examine your child because sometimes serious infections such as pneumonia can develop. In such cases, antibiotics may be needed to treat the infection.