Croup is a common respiratory problem in young children. It tends to occur in the fall and winter. Its main symptom is a harsh, barking cough. Croup causes swelling and narrowing in the voice box, windpipe, and breathing tubes that lead to the lungs. This can make it hard for your child to breathe. An attack of croup can be scary, but it is rarely serious. Children usually get better in several days with rest and care at home.