According to WebMD, croup is excessively contagious for children, particularly those between 3 months and 6 years old. This is because these children have tinier windpipes and bronchial passages that are more likely to be blocked. Croup is spread when a child coughs and sends droplets through the air.
KidsHealth says that croup cases tend to cluster in the fall and winter due to peak season for the viruses that cause it. WebMD says that most croup cases are not serious and can be treated at home. Croup tends to run its course in five or six days. In serious cases, hospitalization may be required.