1. Participant is < 21 years of age 2. Parent/ Legal Guardian/ Adult Participant can understand the consent process and is willing to provide informed consent/HIPAA: 3. (a) Participant is receiving one or more of the study drugs of interest at the time of enrollment or (b) Participant is NOT receiving one or more of the study drugs of interest but is SARS-COV-2 positive within 60 days prior to enrollment 1. Participant has a known pregnancy Below exclusion criteria apply only to: Participants receiving one or more of the study drugs of interest at the time of enrollment, DOI administration or PK sampling: (Refer to DOI specific appendices for details on enrollment cohort specifications and additional eligibility criteria) 2. Has had intermittent dialysis within previous 24 hours 3. Has had a kidney transplant within previous 30 days 4. Has had a liver transplant within previous 1 year 5. Has had a stem cell transplant within previous 1 year 6. Has had therapeutic hypothermia within previous 24 hours 7. Has had plasmapheresis within the previous 24 hours 8. Has a Ventricular Assist Device 9. Has any condition which would make the participant, in the opinion of the investigator, unsuitable for the study

• All B-ALL patients must be enrolled on APEC14B1 and consented to Eligibility Screening (Part A) prior to treatment and enrollment on AALL1731. APEC 14B1 is not a requirement for B-LLy patients. B-LLy patients may directly enroll on AALL1731.
• Age at diagnosis:
• Patients must be >= 365 days and < 10 years of age (B-ALL patients without DS).
• Patients must be >= 365 days and =< 31 years of age (B-ALL patients with DS).
• Patients must be >= 365 days and =< 31 years of age (B-LLy patients with or without DS).
• B-ALL patients without DS must have an initial white blood cell count < 50,000/uL (performed within 7 days prior to enrollment).
• B-ALL patients with DS are eligible regardless of the presenting white blood cell count (WBC) (performed within 7 days prior to enrollment).
• Patient has newly diagnosed B-cell ALL, with or without Down syndrome: > 25% blasts on a bone marrow (BM) aspirate;
• OR if a BM aspirate is not obtained or is not diagnostic of B-ALL, the diagnosis can be established by a pathologic diagnosis of B-ALL on a BM biopsy;
• OR a complete blood count (CBC) documenting the presence of at least 1,000/uL circulating leukemic cells;
• OR patient has newly diagnosed B-cell LLy Murphy stages I or II, with or without Down syndrome.
• Note: For B-LLy patients with tissue available for flow cytometry, the criterion for diagnosis should be analogous to B-ALL. For tissue processed by other means (i.e., paraffin blocks), the methodology and criteria for immunophenotypic analysis to establish the diagnosis of B-LLy defined by the submitting institution will be accepted (diagnostic biopsy for B-LLy must be performed within 14 days prior to enrollment).
• All patients and/or their parents or legal guardians must sign a written informed consent.
• All institutional, Food and Drug Administration (FDA), and National Cancer Institute (NCI) requirements for human studies must be met.
• Patient must not have secondary ALL that developed after treatment of a prior malignancy with cytotoxic chemotherapy. Note: patients with Down syndrome with a prior history of transient myeloproliferative disease (TMD) are not considered to have had a prior malignancy. They would therefore be eligible whether or not the TMD was treated with cytarabine.
• With the exception of steroid pretreatment or the administration of intrathecal cytarabine, patients must not have received any prior cytotoxic chemotherapy for either the current diagnosis of B ALL or B LLy or for any cancer diagnosed prior to initiation of protocol therapy on AALL1731.
• For patients receiving steroid pretreatment, the following additional exclusion criteria apply:
• Non-DS B-ALL patients must not have received steroids for more than 24 hours in the 2 weeks prior to diagnosis without a CBC obtained within 3 days prior to initiation of the steroids.
• DS and non-DS B-LLy patients must not have received > 48 hours of oral or IV steroids within 4 weeks of diagnosis.
• Patients who have received > 72 hours of hydroxyurea within 1 week (7 days) prior to the start of systemic protocol therapy.
• B-ALL patients who do not have sufficient diagnostic bone marrow submitted for APEC14B1 diagnostic testing and who do not have a peripheral blood sample submitted containing > 1,000/uL circulating leukemia cells.
• Patient must not have acute undifferentiated leukemia (AUL).
• Non-DS B-ALL patients with central nervous system [CNS]3 leukemia (CNS status must be known prior to enrollment).
• Note: DS patients with CNS3 disease are eligible but will be assigned to the DS-High B-ALL arm. CNS status must be determined based on a sample obtained prior to administration of any systemic or intrathecal chemotherapy, except for steroid pretreatment.
• Non-DS B-ALL patients with testicular leukemia. (Note: DS patients with testicular disease are eligible but will be assigned to the DS-High B-ALL arm).
• For LLy patients, the following additional exclusion criteria apply:
• T-Lymphoblastic Lymphoma.
• Morphologically unclassifiable lymphoma.
• Absence of both B-cell and T-cell phenotype markers in a case submitted as lymphoblastic lymphoma.
• CNS positive disease or testicular involvement.
• M2 (5%
•25% blasts) or M3 (> 25% blasts) marrow.
• Patients with known Charcot-Marie-Tooth disease.
• Patients with known MYC translocation associated with mature (Burkitt) B-cell ALL, regardless of blast immunophenotype.
• Patients requiring radiation at diagnosis.
• Female patients who are pregnant since fetal toxicities and teratogenic effects have been noted for several of the study drugs. A pregnancy test is required for female patients of childbearing potential.
• Lactating females who plan to breastfeed their infants.
• Sexually active patients of reproductive potential who have not agreed to use an effective contraceptive method for the duration of their study participation.

• Patients must be less than 22 years of age at the time of study enrollment
• Patient must have one of the following:
• Patient has known or suspected relapsed/refractory (including primary refractory) AML
• This includes isolated myeloid sarcoma
• Patient has known or suspected relapsed/refractory (including primary refractory) myeloid leukemia of Down syndrome
• Patient has known or suspected relapsed ALL that meets one of the following criteria:
• Second or greater B-ALL medullary relapse, excluding KMT2Ar.
• Any first or greater B-ALL medullary relapse involving KMT2Ar.
• Any first or greater T-ALL medullary relapse with or without KMT2Ar.
• Patient has known or suspected relapsed/refractory (including primary refractory) mixed phenotype acute leukemia (MPAL)
• Patient has known or suspected de novo or relapsed/refractory (including primary refractory) treatment-related AML (t-AML) or treatment-related myelodysplastic syndrome (t-MDS)
• Patient has known or suspected de novo or relapsed/refractory (including primary refractory) myelodysplastic syndrome (MDS)
• Patient has known or suspected de novo or relapsed/refractory (including primary refractory) juvenile myelomonocytic leukemia (JMML)
• All patients and/or their parents or legal guardians must sign a written informed consent
• All institutional, Food and Drug Administration (FDA), and National Cancer Institute (NCI) requirements for human studies must be met