Listen to Sacrum Mysterium: Part II "Song of Mary", What Child Is This? online. Sacrum Mysterium: Part II "Song of Mary", What Child Is This? is an English language song and is sung by Apollo's Fire, Meredith Hall, Ensemble La Nef and Sylvain Bergeron. Sacrum Mysterium: Part II "Song of Mary", What Child Is This?, from the album Sacrum Mysterium (A Celtic Christmas Vespers), was released in the year 2012. The duration of the song is 3:40. Download English songs online from JioSaavn.