DISEASE CHARACTERISTICS: Histologically or cytologically proven recurrent or refractory solid tumors No leukemia Patients with brain tumors are not eligible until the first 2 patients at each dose level are evaluable for toxicity

PATIENT CHARACTERISTICS: Age: 21 and under Performance status: Karnofsky 50-100% Lansky play scale 50-100% (for infants) Life expectancy: At least 8 weeks Hematopoietic: Absolute neutrophil count at least 1,000/mm3 Hemoglobin at least 9 g/dL Platelet count at least 75,000/mm3 Hepatic: Bilirubin less than 1.5 mg/dL SGPT less than 5 times upper limit of normal Renal: Creatinine normal for age OR GFR at least 70 mL/min Cardiovascular: Cardiac shortening fraction at least 27% OR institutional normal OR Cardiac ejection fraction greater than 50% OR institutional normal Neurologic: Neurologic deficits in patients with CNS tumors must be stable for at least 2 weeks Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 6 months after the study No uncontrolled infection

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 1 week since prior growth factor therapy and recovered At least 6 months since prior bone marrow transplantation and no evidence of graft versus host disease Chemotherapy: At least 2 weeks since prior myelosuppressive chemotherapy and recovered At least 6 weeks since prior nitrosourea and recovered At least 2 weeks on stable dexamethasone for patients with CNS tumors No concurrent chemotherapy Endocrine therapy Not specified Radiotherapy: At least 2 weeks since prior palliative radiotherapy (small port) At least 6 months since prior substantial bone marrow radiation At least 6 months since total abdominal, pelvic, chest, mantle, and Y ports radiotherapy Surgery: Not specified Other: No other concurrent anticancer therapy or investigational agents