Vinblastine and Carboplatin in Treating Young Patients With Newly Diagnosed or Recurrent Low-Grade Glioma

DISEASE CHARACTERISTICS: * Histologically confirmed\* low-grade glioma, including 1 of the following subtypes: * Astrocytoma variants * Fibrillary, protoplasmic, or mixed * Pilocytic astrocytoma, including pilomyxoid variants * Pleomorphic xanthoastrocytoma * Infantile desmoplastic astrocytoma * Ganglioglioma * Oligodendroglial tumors * Mixed glioma, including oligoastrocytoma NOTE: \*Biopsy not required for patients who have visual pathway tumors involving the optic nerves and/or optic radiations (i.e., not isolated to the hypothalamus/chiasm) * Biopsy proven focal low-grade gliomas of the brainstem with measurable disease allowed * No diffuse, intrinsic brainstem tumors * Residual tumor visible on MRI * Patients without NF-1 must meet the following criteria: * Progressive disease after surgery/biopsy based on clear radiographic or clinical evidence of progression OR gross residual tumor (\> 1.5 cm²) after surgery/biopsy that is felt to be a high risk to the patient for neurologic and/or visual impairment if the tumor progresses * Visual pathway tumors that are not isolated to the hypothalamus/chiasm and are not biopsied must be a high risk to the patient for neurologic and/or visual impairment * Patients with NF-1 must have evidence of radiographic progression on MRI and/or clinical worsening (e.g., worsening of ophthalmologic exam for visual pathway tumors) * Meets 1 of the following criteria: * Newly diagnosed disease * Recurrent disease * No ventriculoperitoneal shunt-related ascites PATIENT CHARACTERISTICS: * Karnofsky performance status (PS) 50-100% (for patients \> 10 years of age) OR Lansky PS 50-100% (for patients ≤ 10 years of age) * Absolute neutrophil count ≥ 1,000/mm³ * Platelet count ≥ 100,000/mm³ (transfusion independent) * Hemoglobin ≥ 8.0 g/dL (RBC transfusions allowed) * Creatinine clearance or radioisotope glomerular filtration rate ≥ 70 mL/min OR creatinine based on age, as follows: * No greater than 0.8 mg/dL (for patients ≤ 5 years of age) * No greater than 1.0 mg/dL (for patients 6-10 years of age) * No greater than 1.2 mg/dL (for patients 11-15 years of age) * No greater than 1.5 mg/dL (for patients \> 15 years of age) * Bilirubin ≤ 1.5 times upper limit of normal * ALT ≤ 110 U/L * Albumin ≥ 2 g/dL * No history of allergy to carboplatin * No hyponatremia requiring treatment * No uncontrolled infection * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No prior therapy except for corticosteroids and surgery (for patients with newly diagnosed disease) * Prior chemotherapy and/or radiotherapy in addition to surgery and corticosteroids allowed (for patients with recurrent disease) * Prior carboplatin and/or vinblastine allowed if there was no evidence of progressive disease while on therapy and there were no dose reductions due to toxicity (for patients with recurrent disease) * At least 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas) and recovered (for patients with recurrent disease) * At least 7 days since prior hematopoietic growth factors (for patients with recurrent disease) * At least 7 days since prior biological agents (for patients with recurrent disease) * At least 9 months since prior external beam radiotherapy or gamma knife therapy that included all target lesions (i.e., there is no restriction if a new lesion arises outside the radiation field or a nonirradiated lesion progresses) and recovered (for patients with recurrent disease) * No other concurrent investigational drugs * No other concurrent anticancer agents * No other concurrent chemotherapy, radiotherapy, immunotherapy, or biological therapy * No concurrent corticosteroids for antiemesis * Concurrent steroids allowed for tumor edema/increased intracranial pressure provided dose of dexamethasone is stable or decreasing for the past 7 days * Concurrent physiologic or stress doses of steroids allowed for endocrine deficiencies