This phase II trial tests the safety and best dose of revumenib in combination with chemotherapy, and evaluates whether this treatment improves the outcome in infants and young children who have leukemia that has come back (relapsed) or does not respond to treatment (refractory) and is associated with a KMT2A (MLL) gene rearrangement (KMT2A-R). Leukemia is a cancer of the white blood cells, where too many underdeveloped (abnormal) white blood cells, called "blasts", are found in the bone marrow, which is the soft, spongy center of the bones that produces the three major blood cells: white blood cells to fight infection; red blood cells that carry oxygen; and platelets that help blood clot and stop bleeding. The blasts crowd out the normal blood cells in the bone marrow and spread to the blood. They can also spread to the brain, spinal cord, and/or other organs of the body. The leukemia cells of some children have a genetic change in which a gene (KMT2A) is broken and combined with other genes that typically do not interact with one another; this is called "rearranged". This genetic rearrangement alters how other genes are turned on or off in the cell, turning on genes that drive the development of leukemia. Patients with KMT2A rearrangement have higher risk for cancer coming back after treatment. Revumenib is an oral medicine that directly targets the changes that occur in a cell with a KMT2A rearrangement and has been shown to specifically kill these leukemia cells in preclinical laboratory settings and in animals. Drugs used in chemotherapy, such as vincristine, prednisone, asparaginase, fludarabine and cytarabine work in different ways to stop the growth of cancer cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. This trial is being done to find out if the combination of revumenib and chemotherapy would be safe and/or effective in treating infants and young children with relapsed or refractory KMT2A-R leukemia.