Irinotecan in Treating Children With Refractory Solid Tumors

Inclusion Criteria: * Histologically or cytologically confirmed CNS or solid tumors recurrent or refractory to standard therapy * Solid tumors: * Neuroblastoma * Ewing's Sarcoma/peripheral primitive neuroectodermal tumor (PNET) * Osteosarcoma * Rhabdomyosarcoma * Other extracranial solid tumors * CNS tumors: * Medulloblastoma/PNET * Ependymoma * Brain stem glioma * Other CNS tumor * Intrinsic brain stem tumor (biopsy required only if previously treated with radiosurgery) * Classic optic glioma (histologic requirement waived) * Measurable disease by imaging studies * No lesions assessable only by radionuclide scan * Previously irradiated lesions used to evaluate tumor response must show evidence of an interim increase in size * Performance status - Karnofsky 50-100% if more than 10 years old * Performance status - Lansky 50-100% if 10 years or younger * At least 8 weeks * Absolute neutrophil count greater than 1,000/mm\^3 * Platelet count greater than 100,000/mm\^3 * Hemoglobin greater than 8 mg/dL * Inadequate peripheral blood counts due to bone marrow infiltration allowed * Bilirubin no greater than 1.5 mg/dL * SGPT less than 5 times normal * Creatinine normal * Glomerular filtration rate at least 70 mL/min * No severe uncontrolled infection * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 6 months after study * At least 3 weeks since prior immunotherapy and recovered * No concurrent biologic therapy * At least 3 weeks since prior chemotherapy (8 weeks since prior nitrosoureas) and recovered * No more than 2 prior chemotherapy regimens * No other concurrent chemotherapy * Prior topotecan allowed * No prior irinotecan * Concurrent dexamethasone for brain tumor patients allowed if on a stable or decreasing dose for at least 2 weeks prior to study * At least 3 weeks since prior endocrine therapy * No other concurrent endocrine therapy * See Disease Characteristics * At least 8 weeks since prior extended radiotherapy (including evaluable lesions) and recovered * No prior total body radiotherapy * No concurrent radiotherapy * See Disease Characteristics * At least 3 weeks since prior investigational agents * No other concurrent investigational agents * No concurrent anticonvulsants * No concurrent medications that would interfere with the P-450 enzyme system function (e.g., erythromycin, cimetidine, fluconazole)