Who is Mother and Father from Z for Zachariah and what is their importance?

Ann lived in the valley with her mother and father before the war. Ann's father went to the nearest town after the phones stopped working to learn what had happened. Ann's father came back with stories of death and devastation. A short time later, Ann's parents decided to travel in the opposite direction to find survivors. They never come back. However, Ann uses all her parents taught her to survive alone in the valley.