This is a prospective randomized trial of pediatric patients in the emergency department (ED) or inpatient ward diagnosed with acute pancreatitis. Patients meeting the study inclusion criteria will be identified by an ED or inpatient physician. The ED or inpatient physician will ask the eligible patient/parent if they are interested in hearing about the study. If the eligible patient/parent is interested in hearing information about the study, the ED or inpatient ward will notify the PI via telephone or page. The PI will come to the eligible patient's room to explain the study and answer any questions, or the PI will page a research team member to do so. If the patient/parent agrees to participate in the study, the research team member will consent the parents of the patients aged 0-17 years or consent patients aged 18 years. Assent will be obtained from patients aged 8-17 years. Non-English speaking patients/parents will be consented using an in-person translator or the blue phone translating service. These consent and assent forms will be signed by a witness. At the time of enrollment, the subject identification (ID) number and medical record number will be entered into the electronic Subject ID Key. Once the patient is enrolled in the study, their treatment will be randomized to either the LR or the NS group. Both treatments are current standard of care for acute pancreatitis. Patients who choose not to participate in the study will receive the standard of care treatment at the discretion of the attending physician, which may involve either fluid, and will likely include most (if not all) of the lab studies as outlined in this protocol.