We report a case of a previously healthy 9-year-old boy who presented to the emergency department following accidental ingestion of 35% hydrogen peroxide. He developed emesis and mild abdominal pain and was found to have extensive portal venous gas, severe gastric pneumatosis, and free intraperitoneal air on a computed tomography scan. He was transferred to an outside hospital for hyperbaric oxygen therapy, with no emergency surgical intervention indicated. This case highlights the dangers of ingesting even a small amount of concentrated hydrogen peroxide in children and underscores the safe storage practices at home.