A Study of Sonrotoclax (BGB-11417) in Children With Relapsed or Refractory Acute Myeloid Leukemia and B-cell Acute Lymphoblastic Leukemia

The goal of this clinical trial is to learn if sonrotoclax (BGB-11417) is safe and may help treat children and adolescents with acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL) that has come back after treatment or has not responded to treatment. The study will also learn how the body processes sonrotoclax when it is given with other medicines. The main questions it aims to answer are: * Is sonrotoclax safe and well tolerated when given with other anti-cancer medicines? * How does the body absorb, process, and remove sonrotoclax? * Does treatment with sonrotoclax, in combination with other medicines, help reduce or eliminate leukemia? Researchers will give sonrotoclax together with other anti-cancer medicines to participants with relapsed or refractory AML or ALL. Participants will: * Take sonrotoclax in combination with other anti-cancer medicines * Have regular clinic visits for physical exams, blood tests, heart monitoring, and other safety assessments. * Provide blood samples to measure how the body processes sonrotoclax. * Have tests to evaluate how their leukemia responds to treatment. * Continue treatment as long as it is helping and side effects remain manageable, according to the study plan.

Key Inclusion Criteria Participants must meet all of the following criteria to be eligible for participation: 1. Have a performance status of Lansky ≥50 for participants ≤16 years of age or Karnofsky ≥50 for participants \>16 years of age. 2. Have adequate renal function, defined as an estimated or measured glomerular filtration rate (GFR) ≥60 mL/min. 3. Have adequate hepatic function, defined as: * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \