PATIENT CHARACTERISTICS: Age: 21 and under Performance status: Not specified Life expectancy: Not specified Hematopoietic: Not specified Hepatic: No active hepatitis B or C Bilirubin no greater than 1.5 times normal Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) less than 2.5 times normal Renal: Creatinine no greater than 1.5 times normal OR Creatinine clearance at least 65 mL/min Cardiovascular: Shortening fraction greater than 27% by echocardiogram OR Ejection fraction greater than 47% by radionuclide angiogram Pulmonary: [1] forced expiratory volume at one second (FEV1)/forced vital capacity (FVC) greater than 60% For uncooperative children: No evidence of dyspnea at rest No exercise intolerance Pulse oximetry greater than 94% Other: No active infection No occult untreated infection HIV negative Not eligible for Children's Cancer Group (CCG) or Pediatric Oncology Group (POG) transplant study Donor criteria: Genotypically matched sibling or phenotypically matched family member (bone marrow or peripheral blood stem cells may be used) One antigen mismatched related donor Matched or one antigen mismatched unrelated donor Cord blood (genotypic or phenotypic match or one antigen mismatch) Matched sibling or phenotypically matched family member peripheral stem cells