A 5-month-old boy is brought to the emergency department in December with 3 days of runny nose, cough, and worsening rapid breathing. He was born at term and is otherwise healthy. Temperature is 38.1 C, pulse is 150/min, respirations are 60/min, and oxygen saturation is 93% on room air. Examination shows nasal flaring, mild intercostal retractions, diffuse expiratory wheezes, and fine crackles bilaterally. He is feeding about half his usual amount and has adequate wet diapers. Which of the following is the most appropriate management?