Regimen 1 Chemotherapy - Those children with a normal CSF flow study at the beginning of the study will receive Regimen 1 chemotherapy along with mafosfamide. Those children with an abnormal CSF flow study will receive Regimen 1 without mafosfamide and a repeat CSF flow study will be performed at the completion of the first 10 weeks of treatment. If the CSF study reflects normal CSF flow, then intrathecal mafosfamide will be given during the second 10 weeks of Regimen 1. Regimen 1 is divided into two courses. Each course lasts about 10 weeks, for a total of 20 weeks of treatment. During Regimen 1 the patient will receive three medications (cyclophosphamide, vincristine, and cisplatin) that are given through the central venous line. The patient will also receive one medication that is given by mouth (etoposide). Cyclophosphamide, vincristine, cisplatin, and etoposide are all anticancer drugs that have been useful in the treatment of brain tumors.