Chemotherapy and radiation used in patients undergoing bone marrow transplant (BMT) disrupts the endothelial lining (a thin layer of cells inside the blood vessels) which is found all throughout the body including the kidney, heart, lungs, and intestines. Disruption of this endothelial lining can lead to complications such as graft-vs-host disease (GVHD), thrombotic microangiopathy (TMA) and veno-occlusive disease (VOD). The purpose of this research study is to help investigators see if pravastatin is safe and well tolerated in patients undergoing BMT to see if it will reduce endothelial injury after BMT. The investigator hypothesizes that prophylactic pravastatin in pediatric allogeneic hematopoietic stem cell transplant recipients with elevated BMI is safe and feasible.