This phase III trial is studying how well combination chemotherapy followed by second-look surgery and radiation therapy works in treating children with nonmetastatic medulloblastoma or primitive neuroectodermal tumor. Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining more than one drug and combining chemotherapy with surgery and radiation therapy may kill more tumor cells.