'Black Nativity,' a folk-song rendering of the Christian story based on Langston Hughes's gospel song-play about the birth of Christ, has become an annual tradition in Boston since 1969. First presented in the Elma Lewis School of Fine Arts, it has attracted a wider audience in its performances on stage at Northeastern University and most recently at the Opera House in Boston. Members of an all-Black professional cast under the musical direction of John Andrew Ross wed their talents with the voices of children as young as five, appearing on stage for the first time.