Risk-Adapted Therapy for Young Children With Embryonal Brain Tumors, Choroid Plexus Carcinoma, High Grade Glioma or Ependymoma

Histologically confirmed newly diagnosed CNS tumors of any of the following : * Medulloblastoma (all histologic subtypes, including medullomyoblastoma and melanotic medulloblastoma) * Supratentorial primitive neuroectodermal tumor (PNET) (including CNS neuroblastoma or ganglioneuroblastoma, medulloepithelioma, and ependymoblastoma) * Pineoblastoma * Atypical teratoid rhabdoid tumor (ATRT) * Choroid plexus carcinoma * High grade glioma (including anaplastic astrocytoma, anaplastic oligodendroglioma, anaplastic ganglioglioma, pleomorphic xanthoastrocytoma with anaplastic features, high-grade astroblastoma , anaplastic pilocytic astrocytoma, malignant glioneuronal tumor, glioblastoma multiforme), or gliosarcoma, * Ependymoma (including all ependymoma histological variants) * Age \< 3 years at time of diagnosis for all histological diagnosis. Medulloblastoma patients ≥ 3 and \< 5years old at diagnosis who have non-metastatic disease with no more than 1cm2 of residual tumor are also eligible. * Meets criteria for 1 of the following risk groups: * Low-risk group: * Histologically confirmed nodular desmoplastic medulloblastoma, including medulloblastoma with extensive nodularity * Focal areas of anaplasia or other atypical features suggesting more aggressive phenotype in a tumor otherwise considered nodular desmoplastic should be treated on the intermediate-risk group, with final risk stratification at the discretion of principal investigator and study pathologist * No evidence of CNS metastasis 7 to 28 days after surgery by MRI and cytologic examination of lumbar cerebrospinal fluid (CSF) * Ventricular CSF from a shunt or Ommaya reservoir may be used to rule out M1 disease when lumbar puncture is medically contraindicated * Intermediate-risk group assignment when there is no other evidence of metastasis and CSF sampling is not possible * Gross total resection, defined as residual tumor or imaging abnormality (not definitive for residual tumor) with a size of \< 1 cm2 confirmed on postoperative CT scan or MRI * Brain stem invasion by the tumor in the absence of imaging evidence of residual tumor (tumor size \< 1 cm2) and otherwise meets criteria for the low-risk group, the patient will be classified as low-risk * Desmoplastic medulloblastoma patients who are ≥3 -\<5 years of age will NOT be eligible for the low risk arm of the protocol. * Intermediate-risk group: * Histologically confirmed nodular desmoplastic medulloblastoma with less than gross total resection and no evidence of metastasis * Any eligible histologic diagnosis other than desmoplastic medulloblastoma with no evidence of CNS metastasis * Medulloblastoma patients who are ≥3 and \< 5 yrs of age irrespective of histology and with no evidence of CNS metastasis * High-risk group: * Any eligible histologic diagnosis with evidence of CNS metastasis * Patients with extraneural metastasis are eligible for treatment on the high-risk group PATIENT CHARACTERISTICS: * Lansky performance status ≥ 30 (except for posterior fossa syndrome) * WBC \> 2,000/mm3 * Platelets \> 50,000/mm3 (without support) * Hemoglobin \> 8 g/dL (with or without support) * ANC \> 500/mm3 * Serum creatinine \< 3 times upper limit of normal (ULN) * ALT \< 5 times ULN * Total bilirubin \< 3 times ULN PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No more than 31 days since prior definitive surgery * No prior radiotherapy or chemotherapy other than corticosteroid therapy