Testing the Addition of the Anti-cancer Drug Venetoclax and/or the Anti-cancer Immunotherapy Blinatumomab to the Usual Chemotherapy Treatment for Infants With Newly Diagnosed KMT2A-rearranged or KMT2A-non-rearranged Leukemia

Inclusion Criteria: * All patients must be enrolled on APEC14B1 and consented to eligibility screening (part A) prior to treatment and enrollment on AALL2321 * Infants (aged 365 days or less) on the date of diagnosis are eligible; infants must be \> 36 weeks gestational age at the time of enrollment * Patients must have newly diagnosed B-acute lymphoblastic leukemia (B-ALL, 2017 World Health Organization \[WHO\] classification), also termed B-precursor ALL, or acute leukemia of ambiguous lineage (ALAL), which includes mixed phenotype acute leukemia. For patients with ALAL, the immunophenotype of the leukemia must comprise at least 50% B lineage * Diagnostic immunophenotype: Leukemia cells must express CD19 Exclusion Criteria: * Patients with Down Syndrome * Patients with secondary B-ALL that developed after treatment of a prior malignancy with cytotoxic chemotherapy * Patients must not have received any cytotoxic chemotherapy for either the current diagnosis of infant ALL or for any cancer diagnosis prior to the initiation of protocol therapy, with the exception of: * Steroid pretreatment: * PredniSONE, prednisoLONE, or methylPREDNISolone for ≤ 72 hours (3 days) in the 7 days prior to enrollment. The dose of predniSONE, prednisoLONE or methylPREDNISolone does not affect eligibility * Inhaled and topical steroids are not considered pretreatment * Note: Pretreatment with dexamethasone in the 28 days prior to initiation of protocol therapy is not allowed wi…