OUTLINE: This is a multicenter study. Patients are stratified according to age in years (1 to 2 vs 3 to 11 vs 12 to 16), type of hematopoietic stem cell transplantation (HSCT) (autologous vs allogeneic), conditioning regimen (either total-body irradiation [TBI] or melphalan vs neither TBI nor melphalan). Patients are randomized to 1 of 2 treatment arms.