HLA-Nonidentical Stem Cell and Natural Killer Cell Transplantation for Children Less the Two Years of Age With Hematologic Malignancies

Secondary objectives for this study include the following: * To estimate the incidence of three transplant-related adverse outcomes (i.e., regimen-related mortality, engraftment failure, and fatal acute GVHD) in the first 100 days after transplantation. * To estimate the incidence of chronic graft-versus-host disease. * To evaluate those factors that affect one-year survival. * To assess the kinetics of lymphohematopoietic reconstitution. * To assess the frequency and clinical relevance of minimal residual disease (MRD) before and after transplantation. * To evaluate the incidence of and risk factors for long-term neurocognitive deficit and organ dysfunction.