Bronchiolitis is a viral infection of the lungs, which affects primarily infants and toddlers. Some or all of the following symptoms are present with bronchiolitis. 1  Wheezing: a high-pitched whistling noise when your child breathes out. 2  You may actually hear this yourself, or a physician may hear wheezing when she listens to your child. 3  Rapid breathing: at a rate of 40 breaths per minute or faster.