This is a randomized, double-blind study that consists of two parts. In Part 1, the study will consist of 3 phases: a 14-day screening phase, a double-blind treatment phase of 12 weeks comparing two doses of study drug (0.5 mg/kg or 1.0 mg/kg groups based on patient's body weight), and an end-of-study or early withdrawal phase followed by Part 2, which consists a of double-blind treatment continuation for patients who have achieved healing during the short-term double-blind treatment phase. The double-blind maintenance treatment phase lasts for not more than 24 weeks and is concluded by an end-of-study/early withdrawal visit. During Part 1, patients will be screened and the diagnosis of erosive and non-erosive Gastroesophageal Reflux Disease (GERD) will be made based on clinical symptoms and confirmed by endoscopy/histology after a biopsy. Patients enrolled in the study will receive study drug once daily for 12 weeks. Each day, the parent/caregiver will record the presence and severity of pre-specified GERD symptoms. At Weeks 4 and 8, the investigator will evaluate the response to treatment by assessment of the GERD symptoms. At Week 12, the investigator will perform an endoscopy of the esophagus with a biopsy to confirm that histological healing has occurred. If a patient continues, additional study drug will be dispensed (at the same dose taken during the short-term double-blind treatment phase) and the patient will be scheduled to return every 8 weeks until study drug is discontinued at Week 24 (Part 2) of the double-blind maintenance treatment phase. At the final visit of the maintenance treatment phase Week 24 (Part 2), assessments including an endoscopy of the esophagus with a biopsy be performed for each patient. Assessments of effectiveness include endoscopic and histological grading of biopsy samples, GERD symptom and severity score (symptoms and severity rated daily by the parent/caregiver in an electronic diary), overall GERD symptom relief, Clinical Global Impression of Improvement (CGI-I) score, and the Global Treatment Satisfaction Score. Safety assessments will include the monitoring of concomitant therapies and adverse events throughout the study, clinical laboratory testing (including hematology, clinical chemistry, urinalysis), vital signs, and physical examination including height, weight, and Tanner staging. Oral rabeprazole 2.5 capsules or 5 mg capsules, given once daily at a dose of 0.5 mg/kg or 1.0 mg/kg; short-term treatment phase is 12 weeks; long-term maintenance treatment phase is 24 weeks.