Bronchiolitis, a lower respiratory tract infection, commonly affects infants and children younger than 2 years. Respiratory syncytial virus is the most common cause. Nasal congestion, rhinorrhea, and mild fever occur in the first 1 to 3 days. Symptoms worsen for several days to include wheezing and other lower respiratory tract signs, and then resolve over days to weeks. However, some children develop hypoxemia and/or respiratory distress and require hospitalization. The diagnosis is clinical, based on the history and physical examination findings. Routine chest x-rays and blood tests are not recommended. Management is supportive, including nasal suctioning, oxygen (in cases of hypoxemia), and hydration. Use of bronchodilators (ie, albuterol, epinephrine) and systemic corticosteroids is not recommended in infants and children ages 1 to 23 months. Pneumonia, another common infection in infants and children, typically is caused by viruses or bacteria. The diagnosis is clinical, and chest x-rays and blood cultures are not required for patients well enough to be treated as outpatients. Antibiotics are not routinely required for preschool-aged children (ie, younger than 5 years) with pneumonia because most have viral infections. For immunized school-aged children with mild to moderate pneumonia suspected to be of bacterial origin, amoxicillin is recommended. In school-aged children, if atypical pathogens (eg, Mycoplasma) are suspected, a macrolide antibiotic should be prescribed.