Shmerke Kaczerginski and Rachela Melezin, two key figures in the story of "The Lonely Child," appear in the new the new documentary about the song and its role in history. (13th Gen) A Yiddish word for destiny or fate, beshert, carries a positive, even blessed connotation. It’s a term that comes up repeatedly in the new documentary “The Lonely Child,” a sprawling tale that follows the trail of a lullaby written in the Vilna Ghetto during the Holocaust about a daughter separated from her mother. The song’s grim origins might sound like a bad fit for beshert encounters, but this...