 Children will be excluded if they have any of the following: cystic fibrosis, anatomic lung disease, bronchiectasis, congenital heart disease, history of repeated aspiration or velopharyngeal incompetence, malignancy, conditions requiring treatment with immune suppressants, primary immunodeficiency, advanced HIV infection, prolonged admissions 48 h to hospital within the past 2 months, pneumonia previously diagnosed within the past month, lung abscess diagnosed within the past six months, receipt of 24 hours of beta-lactam antibiotic therapy already received at presentation to the ED, receipt of at least a 5 day course of amoxicillin 72h prior to presenting to the ED, receipt of an intravenous cephalosporin or azithromycin in the ED, or suspected allergy to penicillin. Children will not be eligible to participate more than once. 