Isolation
The Golden Age hospital is described as standing "alone, bounded by four flat roads, like an island, which in its present incarnation seemed to symbolize its apartness, a natural quarantine." As such, the hospital itself symbolizes the feelings of isolation many of the characters feel.
The isolation ward
When Frank is diagnosed with polio he is sent to the isolation ward. This is a scary experience for him, causing fear and loneliness. The children are isolated from their loved ones and are forced to endure the pain of their illness by themselves. As such, for Frank, the isolation ward is a symbol of fear, trauma and loneliness.
Growing up
In the novel, London frequently writes about how the experience of illness in childhood makes a child grow up faster. For example, Elsa's mother thinks that "each time she saw her, [she] had become more adult. She had lost her childhood."
Frank and Elsa
The romance between Frank and Elsa represents an escape and respite from their individual struggle with illness. They can also relate to each other, which is something they both cannot do with their families as easily since becoming ill.
Music
For Frank's family, music is an escape from their own struggles and feelings of alienation in their new country. Frank's mother is described as being "distance from him" when she is playing the piano, which suggests she has transcended her own life through immersion in music.
