You may be thinking of technology that allows us to use stem cells from bone marrow for things like reproductive assistance or human cloning. (Stem cells are a type of young cell that is capable of developing into many, or even all, of the different cell types our bodies need.)
Right now, there’s no such thing as a “bone marrow baby.” We don’t have the science and technology yet to use bone marrow stem cells in that way. It’s possible that we might in the future, but we still need to do a lot of research and gain a lot of understanding before we can take that step. We also need to carefully consider the risks and ethics involved before we try.