William Butler Yeats married late in life, in 1917, when he was already 52 years old.  The marriage marked a crucial turn in Yeats's life, not so much because he had married the woman of his dreams--that was Maud Gonne, and she had rejected him enough times by 1917 that he knew he would never achieve his dream of marrying her--but more because the marriage brought Yeats into a different relation to the world:  he now was a man of family, and when his first child, a daughter, was born to him in 1919 he knew that his sense of himself and his role in the world had altered forever.

Yeats was already consumed with the greatest fear a parent can feel:  the fear of a child's death.  His dearest friend, Lady Gregory, had in 1918 learned that her only son, Robert, had been killed in World War I.  Yeats responded to her awful grief with one of the great elegies in English poetry, "In Memory of Major Robert Gregory."  This fear of being unable to protect one's own child haunted him when his own daughter, Anne, was born in 1919, and it informs the opening of "A Prayer for my Daughter":

Yeats expresses great anxiety over the frail protection, the mere "cradle-hood and coverlid," that can only half-hide his frail infant.  The howling wind that comes from the sea itself threatens her security, and the poet has paced and prayed into the night for some protection for her.