Adding Dasatinib Or Venetoclax To Improve Responses In Children With Newly Diagnosed T-Cell Acute Lymphoblastic Leukemia (ALL) Or Lymphoma (T-LLY) Or Mixed Phenotype Acute Leukemia (MPAL)

Inclusion Criteria: * Enrollment on INITIALL. * Age 1-18.99 years at the time of enrollment on INITIALL. * T-Acute lymphoblastic leukemia or lymphoblastic lymphoma or mixed phenotype acute leukemia/ lymphoma * No prior chemotherapy excluding therapy given on or allowed by INITIALL. * Patient has completed no more than 3 days of chemotherapy on INITIALL. * Direct bilirubin ≤ 1.5x the upper limit of normal for age * Alanine aminotransferase (ALT) ≤ 5x the upper limit of normal for age * Calculated glomerular filtration rate (GFR) ≥ 50 mL/min/1.73m\^2 using the Bedside Schwartz equation OR creatinine below or equal to the maximum defined below: * Age: 1 to \< 2 years - Maximum serum creatinine (mg/dL): 0.6 (Male), 0.6 (Female) * Age: 2 to \< 6 years - Maximum serum creatinine (mg/dL): 0.8 (Male), 0.8 (Female) * Age: 6 to \< 10 years - Maximum serum creatinine (mg/dL): 1 (Male), 1 (Female) * Age: 10 to \< 13 years - Maximum serum creatinine (mg/dL): 1.2 (Male), 1.2 (Female) * Age: 13 to \< 16 years - - Maximum serum creatinine (mg/dL): 1.5 (Male), 1.4 (Female) * Age: ≥ 16 years - Maximum serum creatinine (mg/dL): 1.7 (Male), 1.4 (Female) Exclusion Criteria: * Inability or unwillingness to give informed consent/ assent as applicable. * Patients with \> Grade 2 neuropathy at the time of enrollment (participant with T-LLy only). * Documented malabsorption syndrome or any other condition that precludes receipt of oral medications. * Known HIV infection or active hepatitis B (defined as hepatitis B surface antigen-positive) or C (defined as hepatitis C antibody-positive). * Pregnant or lactating. * For patients of reproductive potential, unwillingness to use highly effective contraception for the duration of protocol therapy and for 90 days afterwards. * Receipt of a strong or moderate CYP3A4 inducer such as rifampin, carbamazepine, phenytoin, and St. John's wort within 7 days of the start of protocol treatment. * Consumption of grapefruit, grapefruit products, Seville oranges, or starfruit within 3 days of the start of protocol therapy.