Irinotecan in Treating Children With Refractory or Progressive Solid Tumors

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed solid tumor refractory to standard therapy or for which no known effective therapy exists * Brain tumors eligible * Histologic verification waived for brain stem gliomas * Evaluable disease * No bone marrow involvement PATIENT CHARACTERISTICS: Age: * 1 to 21 Performance status: * Karnofsky 50-100% (over age 10) * Lansky 50-100% (age 10 and under) Life expectancy: * At least 8 weeks Hematopoietic: * Absolute neutrophil count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 8 g/dL Hepatic: * Bilirubin less than 1.5 mg/dL * SGPT less than 5 times normal Renal: * Creatinine normal OR * Glomerular filtration rate at least 70 mL/min Other: * No uncontrolled infection * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 6 months after study PRIOR CONCURRENT THERAPY: Biologic therapy: * At least 6 months since prior autologous bone marrow transplantation (BMT) (not including stem cell rescue after high-dose chemotherapy) * At least 1 week since prior growth factors * No prior BMT with total body irradiation (stratum I) * No prior BMT with or without total body irradiation (stratum 2) * No prior allogeneic BMT (all strata) * No concurrent sargramostim (GM-CSF) * No other concurrent prophylactic growth factor support during the first course of therapy Chemotherapy: * At least 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas) * No prior irinotecan * No more than 2 prior multi-agent chemotherapy regimens (stratum 2) * No other concurrent chemotherapy Endocrine therapy: * Concurrent dexamethasone allowed if on stable or decreasing dose for at least 2 weeks prior to study Radiotherapy: * At least 6 months since prior craniospinal radiotherapy or radiotherapy to 50% or more of the pelvis * At least 6 weeks since other prior substantial bone marrow radiotherapy * No prior central axis radiotherapy, pelvic radiotherapy, and/or total abdominal radiotherapy (stratum 2) Surgery: * Not specified Other: * Recovered from all prior therapy * No other concurrent investigational agents * Concurrent enzyme-inducing anticonvulsants (e.g., phenytoin, phenobarbital, carbamazepine) allowed if on stable dose for at least 2 weeks prior to study (stratum 3) * Concurrent valproic acid allowed if combined with another enzyme inducing anticonvulsant drug (stratum 3)