DELAYED INTENSIFICATION I** (ALL PATIENTS): Patients receive vincristine IV on days 1, 8, 15, 43, and 50; dexamethasone PO or IV BID on days 1-21 for patients age 1-9, or on days 1-7 and 15-21 for patients age >= 10; doxorubicin hydrochloride IV over 15 minutes on days 1, 8, and 15; study drug IV over 1 hour on days 4 and 43; cyclophosphamide IV over 30 minutes on day 29; cytarabine IV or subcutaneously (SC) on days 29-32 and 36-39; thioguanine PO on days 29-42; and methotrexate IT on days 1, 29, and 36. Patients treated as RER proceed to maintenance therapy. Patients treated as SER (i.e., patients with CNS3 disease at diagnosis, or pre-treated with steroids, or who are RERs with mixed lineage leukemia [MLL] gene rearrangements) proceed to interim maintenance II followed by delayed intensification II.