Chemotherapy and Stem Cell Transplantation in Treating Children With Central Nervous System Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed primary central nervous system malignancy * Recurrent, persistent, or progressive disease after at least 1 prior first-line treatment regimen PATIENT CHARACTERISTICS: Age * 18 and under at initial diagnosis Performance status * ECOG 0-2 Life expectancy * At least 8 weeks Hematopoietic * Absolute neutrophil count greater than 750/mm\^3 * WBC greater than 2,500/mm\^3 * Platelet count greater than 100,000/mm\^3 * No underlying myelodysplasia, stem cell disorder, or other inherent hematologic synthetic defect Hepatic * Liver function tests less than 2 times normal OR * Absence of active hepatitis by liver biopsy * Bilirubin less than 1.5 mg/dL Renal * Glomerular filtration rate greater than 60 mL/min by radionucleotide assay Cardiovascular * Ejection fraction at least 45% Pulmonary * Clinically normal pulmonary function (patients 5 years of age and under) * FEV\_1 and FVC at least 50% (patients over 5 years of age) OR * Arterial blood gas normal and DLCO greater than 50% Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No mucositis or mucosal infection * HIV negative PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * At least 3 weeks since prior systemic cytotoxic chemotherapy Endocrine therapy * Not specified Radiotherapy * At least 6 months since prior radiotherapy to the pelvis or spine Surgery * Not specified