Venetoclax Combined With Vyxeos (CPX-351) for Participants With Relapsed or Refractory Acute Leukemia

Inclusion Criteria: * Ages 1 Year to 39 Years * Diagnosis of one of the following: * Acute myeloid leukemia (AML), any subtype except * Patients with acute promyelocytic leukemia (APML) are NOT eligible * Patients with ML-DS are NOT eligible * Myeloid sarcoma * Acute leukemia of ambiguous lineage (ALAL) * Acute undifferentiated leukemia (AUL) * T/myeloid mixed phenotype acute leukemia (MPAL) * B/myeloid MPAL * MPAL with KMT2A-rearrangement MPAL with t (9;22) are NOT eligible * T-cell acute lymphoblastic leukemia (T ALL) * Early thymocyte precursor (ETP) ALL * KMT2A-rearranged ALL * Disease Status * Relapsed/Refractory AML, MPA, and AUL * Untreated therapy related AML * Relapsed/Refractory KMT2A-rearranged ALL, T-cell ALL, ETEP ALL * Karnofsky/Lanksy performance level score of greater than or equal to 50 percent. * Prior therapy requirements * Fully recovered from acute toxicities of Hematopoietic Stem Cell Transplant (HSCT) or Anthracycline Exposure * 14 days must have elapsed since the completion of systemic cytotoxic therapy other than hydroxyurea, decitabine or azacitidine * 2 weeks must have elapsed for local palliative radiotherapy (RT); 6 months must have elapsed if prior craniospinal RT or if 50% radiation of pelvis, and at least 6 weeks must have elapsed if other substantial bone marrow radiation * Adequate renal, liver, cardiac, and central nervous system (CNS) function Exclusion Criteria: * Diagnosis of one of …