Children (less than 10 years of age) are eligible if they have been diagnosed with either a medulloblastoma tumor or CNS embryonal tumors of the brain or spinal cord. The standard approach to the treatment of these brain tumors in young children may include surgery, radiation therapy to the brain and spinal cord and chemotherapy. Radiation therapy is the use of high energy x-rays to kill cancer cells. Chemotherapy means treatment with cancer killing drugs. This research study will compare two different treatment regimens to see which is better for treating children with this type of brain cancer.