RecruitingPhase 2Drug trialA Pilot Study to Evaluate the Feasibility of Post-Hematopoietic Stem Cell Transplant Prophylaxis With Decitabine Combined With Filgrastim for Children and Young Adults With AML, MDS and Related Myeloid MalignanciesThe purpose of this study is to examine if it is feasible to administer decitabine and filgrastim after allogenic hematopoietic stem cell transplant (HCT) in children and young adults with myelodysplastic syndrome, acute myeloid leukemia and related myeloid disorders, and if the treatment is effective in preventing relapse after HCT. The names of the study drugs involved in this study are: * Decitabine (a nucleoside metabolic inhibitor) * Filgrastim (a recombinant granulocyte colony-stimulating factor (G-CSF)