Why are some of the children at the orphanage called "half-orphans" in the novel, Thirteen Doorways, Wolves Behind Them All?

Half-Orphans is the term used to describe those children who live in the orphanage but who have one parent living. Frankie, Toni, and Vito are living under the assumption they are half-orphans, but they later learn that Gaspare has been lying to them and that their mother is alive.