In the U.S., croup is most commonly seen in the fall and winter months, and can spread via coughs or sneezes, as well as by the germs getting on hands, utensils, or toys (via Harvard Health Publishing). Children can also be exposed to croup by a sick classmate or relative. Once a child develops symptoms of croup, they usually present as having a cold compounded by a low-grade fever. However, in most cases, children who develop croup tend to get over the illness fairly quickly without any serious pulmonary issues.
In more serious cases of croup, children can develop a condition known as stridor, which is marked by a whistling sound when breathing, as per PhysicianOne Urgent Care. Stridor itself isn't always an immediate cause for concern, but if it occurs when your child is resting, that can be a sign the croup has become more severe. Parents should also be on the lookout for signs if their child is trying too hard to breathe. Look at the skin by his or her ribs to see if it is tightening when they breathe. Also be aware of signs of sluggishness or sleepiness, which can also indicate difficulty breathing. If any of these symptoms are spotted, you should contact your doctor immediately.