Initial impression of a 2-year-old girl shows her to be alert with mild breathing difficulty during inspiration and pale skin color. On primary assessment, she makes high-pitched inspiratory sounds (mild stridor) when agitated; otherwise, her breathing is quiet. Her SpO2 is 92% on room air, and she has mild inspiratory intercostal retractions. Lung auscultation reveals transmitted upper airway sounds with adequate distal breath sounds bilaterally. Which is the most appropriate initial intervention for this child