DISEASE CHARACTERISTICS: Histologically confirmed recurrent or refractory solid malignant tumors of childhood including: Soft tissue sarcoma Rhabdomyosarcoma Nonrhabdomyosarcoma Extraosseous Ewing's sarcoma CNS tumors Astrocytoma Primitive neuroectodermal tumor Atypical teratoid/rhabdoid tumors Ependymoma Recurrent neuroblastoma Measurable disease No more than 2 prior treatment regimens

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

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 6 months since prior bone marrow transplantation No concurrent immunomodulating agents Chemotherapy: At least 2 weeks since prior chemotherapy (4 weeks for nitrosourea) and recovered No other concurrent chemotherapy Endocrine therapy: No concurrent corticosteroids except for increased intracranial pressure due to CNS tumors Radiotherapy: At least 6 months since prior radiotherapy to craniospinal axis, spine, and/or more than 50% of the bony pelvis Concurrent radiotherapy to localized painful lesions allowed if at least one measurable lesion is not in radiation field Surgery: Not specified Other: No concurrent participation in another CCG, POG, or COG therapeutic study