Randomized phase III trial to compare the effectiveness of different chemotherapy regimens with or without bone marrow transplantation in treating children who have acute myelogenous leukemia or myelodysplastic syndrome. Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Combining chemotherapy with bone marrow transplantation may allow the doctor to give higher doses of chemotherapy drugs and kill more cancer cells. It is not yet known which treatment regimen is more effective for acute myelogenous leukemia or myelodysplastic syndrome