PATIENT CHARACTERISTICS: Age: 21 and under at diagnosis Performance status: ECOG 0-2 Life expectancy: At least 2 months Hematopoietic: For patients with solid tumors (unless marrow involvement): Absolute neutrophil count (ANC) at least 1000/mm3 Platelet count at least 100,000/mm3 (transfusion independent) Hemoglobin at least 10 g/dL (RBC transfusions allowed) For patients post bone marrow transplantation: ANC at least 1,000/mm3 Platelet count at least 50,000/mm3 (transfusion independent) Hemoglobin at least 10 g/dL (RBC transfusions allowed) Hepatic: Total bilirubin no greater than 1.5 times normal SGOT/SGPT less than 2.5 times normal Renal: Creatinine no greater than 1.5 times normal OR Creatinine clearance or radioisotope glomerular filtration rate at least 70 mL/min Neurologic: Seizure disorder allowed if well controlled CNS toxicity no greater than grade 2