Acetylcysteine, Mannitol, Combination Chemotherapy, and Sodium Thiosulfate in Treating Children With Malignant Brain Tumors

DISEASE CHARACTERISTICS: * Histologically confirmed brain tumors, including any of the following: * Brain stem glioma * Primitive neuroectodermal tumor * CNS germ cell tumor * Malignant glioma * Diagnosis based on any of the following: * CT-assisted or stereotactic biopsy * Open biopsy * Surgical resection * Cerebrospinal fluid cytology * Elevated tumor markers * Unequivocal radiographic changes (for patients with brain stem glioma or optic glioma) * All tumor types, except brain stem glioma, must be recurrent * No radiographic signs of intracranial herniation and/or spinal cord block PATIENT CHARACTERISTICS: Performance status * ECOG 0-2 Life expectancy * At least 90 days Hematopoietic * WBC ≥ 2,500/mm\^3 * Absolute granulocyte count ≥ 1,200/mm\^3 * Platelet count ≥ 100,000/mm\^3 Hepatic * SGOT and SGPT \< 2.5 times upper limit of normal * Bilirubin \< 2.0 mg/dL Renal * Creatinine \< 1.8 mg/dL Pulmonary * No history of clinically significant reactive airway disease Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No significant risk for general anesthesia * No uncontrolled, clinically significant, confounding medical condition within the past 30 days * No contraindication to study drugs PRIOR CONCURRENT THERAPY: Chemotherapy * At least 28 days since prior systemic chemotherapy Radiotherapy * At least 3 months since prior total spine radiotherapy * At least 14 days since …