Under the Bridge — Ellen Kindt McKenzie

When Ritchie's younger sister Rosie gets very sick after their mother suddenly goes away, Rosie begins to receive letters from a lonely troll, and these letters help Ritchie cope with his mother's absence, his father's seeming indifference, and the fifth-grade class bully.In the 1940s American Midwest, Ritchie is coping after his mother suddenly goes away, and his little sister Rosie becomes sick, when a strange letter from a lonely troll comes for Rosie that changes both their lives