ABC PICU is a randomized clinical trial that will compare the clinical consequences of RBC storage duration in 1538 critically ill children nationwide. Laboratory and observational evidence points to concerns about the lack of safety and effectiveness of older RBCs, especially in more vulnerable populations. Physicians and institutions have been systematically transfusing fresh RBCs to some pediatric patients primarily because of beliefs that the use of fresh RBCs improves outcomes. Conversely, the standard practice of blood banks is to deliver the oldest RBC unit in order to decrease blood wastage. To provide much needed high quality evidence to answer the question "do RBCs of reduced storage duration improve outcomes?" The ABC PICU Trial will conduct a RCT comparing development of New or Progressive Multiple Organ Dysfunction Syndrome (NPMODS) in critically ill children transfused with either RBCs stored ≤ 7 days or standard issue RBCs (expected mean RBC storage duration of 17-21 days).