 This is a single institution phase-I pilot study that aims to assess the pharmacokinetics, toxicity and tolerability of CPX-351 in pediatric and young adults with relapsedrefractory hematologic malignancies. Subjects will receive a single course of CPX-351 administered on Days 1, 3, and 5. The study will first open to children in a dose exploration phase, and then be available to an expanded cohort, which will be open to children and young adults once a tolerable dose has been determined. 