Combination Chemotherapy Followed By Peripheral Stem Cell Transplant in Treating Young Patients With Newly Diagnosed Supratentorial Primitive Neuroectodermal Tumors or High-Risk Medulloblastoma

Inclusion Criteria: * High-risk medulloblastoma defined by any of the following: * \> 1.5 cm\^2 residual disease for any medulloblastoma histology, or * Lumbar cerebral spinal fluid (CSF) cytology positive for tumor cells by analysis of fluid collected either before definitive surgery or at least 10 days after definitive surgery unless contraindicated, or * Magnetic resonance imaging (MRI) evidence of M2 or M3 metastatic disease, or * M4 disease * Supratentorial primitive neuroectodermal tumor (PNET) (any M-stage) will be eligible for study entry * Children less than 8 months of age at the time of definitive surgery with or without measurable radiographic residual tumor with M0 stage medulloblastoma will be eligible for study entry * Patients with anaplastic medulloblastoma are eligible regardless of M-stage or residual tumor * Patients with M0 classic, non-desmoplastic medulloblastoma (R1) with radiographically measurable residual disease \< 1.5 cm\^2 are eligible * Cranial MRI (with and without gadolinium) must be done pre-operatively; post-operatively, cranial MRI (with and without gadolinium) must be done, preferably within 48 hours of surgery; entire spinal MRI must be obtained either pre-operatively (with gadolinium) or post-operatively (at least 10 days following surgery) prior to study enrollment (with and without gadolinium); patients with MRI evidence of spinal disease are eligible for this study * Evaluation of lumbar CSF cytology (cytospin preparation fo…