PATIENT CHARACTERISTICS: Age: Under 21 at diagnosis Performance status: ECOG 0-2 Life expectancy: At least 8 weeks Hematopoietic: (unless marrow replaced by tumor) Absolute neutrophil count greater than 500/mm3 Platelet count greater than 50,000/mm3 Hepatic: Bilirubin less than 1.5 mg/dL AST no greater than 2 times normal PT normal Renal: Creatinine less than 1.5 mg/dL OR Creatinine clearance greater than 80 mL/min Urinalysis normal Metabolic: Electrolytes (including calcium, phosphate) normal Glucose normal Weight greater than 10th percentile for age Albumin greater than 3 g/dL Other: No active infection HIV negative Not pregnant or nursing