The purpose of this study is to look at the improvement of a once a day dose of esomeprazole for reducing the signs and symptoms of infants with gastroesophageal reflux disease (GERD). This research study consists of a screening, open-label, and double-blind phase. The screening phase ensures the patient eligibility. No study medication is dispensed during the screening phase. During the open-label phase, patients are administered esomeprazole 2.5mg, 5.0mg or 10.0mg based on his/her weight. During the double-blind phase, the patients are administered either his/her open-label dose or placebo. Double-blind means neither the physician, parent, or patient will know if patient is taking esomeprazole or placebo. The patient will have an equal chance of receiving esomeprazole or placebo.