Who is Ike and Bobby Guthrie from Plainsong and what is their importance?

Ike and Bobby Guthrie are Tom's sons. Ike is the oldest and ten, and Bobby is nine. The boys' situation is heart wrenching, as they have understanding of why their mother no longer seems interested in behaving as a mother. After she abandons the family, they find solace wherever they can, first with the elderly Mrs. Ida Stearns, later with the McPheron brothers.