Croup is a disease that affects infants and young children. It is usually caused by a viral infection in the upper airways. However, it may also be caused by bacteria, allergens or psychological factors. Symptoms of croup include fever, hoarseness, a characteristic barking cough, and stridor (a crowing noise when breathing in). Treatment options include medication, fluid replacement, hospitalization in serious cases. However, croup usually clears up on its own.