This study is exploring a new treatment before a blood or bone marrow transplant to help people with bone marrow failure diseases. It uses a combination of three drugs: Treosulfan, Fludarabine, and rabbit antithymocyte globulin (rATG). These drugs are used in a conditioning regimen to prepare the body for the transplant. Treosulfan and Fludarabine are chemotherapy drugs that help stop cancer cells from growing. rATG helps improve bone marrow function by decreasing the body's immune response. Patients receiving these treatments will have less severe complications after their transplant. The study involves getting these drugs intravenously (IV) over several days and includes follow-ups for a year after the transplant. Participants must be between 1 and 50 years old and have specific medical conditions that can be treated with a transplant.

• Treatment involves several days of IV drug administration.
• Participants are followed up for 1 year post-transplant.
• Eligibility requires specific bone marrow failure diseases.