Donor Stem Cell Transplant in Treating Young Patients With Myelodysplastic Syndrome, Leukemia, Bone Marrow Failure Syndrome, or Severe Immunodeficiency Disease

DISEASE CHARACTERISTICS: * Diagnosis of one of the following: * Acute lymphoblastic leukemia in ≥ 2nd remission or delayed remission induction * High-risk myelodysplastic syndromes * Refractory anemia with excess blasts (RAEB) * RAEB in transformation * Chronic myelogenous leukemia in second chronic phase * No accelerated phase (\> 5% blasts in marrow) * Juvenile myelomonocytic leukemia * Acute nonlymphoblastic leukemia in \> 1st remission or induction failure and \< 30% blasts in marrow * Severe aplastic anemia, defined as absolute neutrophil count \< 500/mm\^3 and platelet and/or red blood cell transfusion dependent * Unresponsive to immunosuppressive therapy * No Fanconi's anemia * Congenital marrow aplasias unresponsive to cytokines and transfusion dependent * Inherited immunodeficiency disease involving neutrophils or lymphocytes, including any of the following: * Chediak-Higashi disease * Wiskott-Aldrich syndrome * Combined immunodeficiency disease (Nezelof's) * Hyper IgM syndrome * No relapsed disease * Haplocompatible related donor, including parent, cousin, aunt, uncle, grandparent, half-sibling, or sibling (≥ 12 years of age), available * 2 or 3 HLA antigen mismatch * At least a 3 HLA antigen genotypic match * No closely matched related or unrelated donor available in sufficient time to do the transplant PATIENT CHARACTERISTICS: * No active hepatitis or cytomegalovirus infection * Cardiac ejection fr…