A 2-year-old child presents to the emergency department with a barking cough, stridor, and a hoarse voice that worsens at night. The child is afebrile but appears anxious and has labored breathing. The nurse suspects croup as the diagnosis. Which of the following interventions should the nurse prioritize to manage the child's symptoms and prevent further respiratory distress?

A. Administer a dose of oral antibiotics to treat the infection is incorrect because most cases of croup are viral in origin (commonly parainfluenza virus). Antibiotics are not indicated unless there is a secondary bacterial infection. B. Place the child in a supine position to facilitate airflow to the lungs is incorrect because lying flat may worsen respiratory distress in a child with croup. Upright positioning is preferred to ease breathing. C. Encourage the child to lie down to conserve energy is incorrect because supine positioning can increase airway obstruction and worsen stridor. Allowing the child to remain upright and calm is safer. D. Provide a cool mist humidifier or take the child outside into cool night air is correct because cool, moist air helps reduce laryngeal inflammation and edema, which can relieve stridor and improve breathing. This is a first-line, noninvasive intervention to manage mild to moderate croup symptoms while minimizing respiratory distress.