Answer:
The tone of "Penguin mania" is lighthearted and playful, as the narrator is gleefully participating in the spontaneous penguin craze that has taken over the city. In contrast, the tone of both "Shelley's Farm" and "Not Going" is more somber and reflective. In "Shelley's Farm", the narrator is looking back on the changes of time, and in "Not Going" the narrator is struggling with the idea of growing up and the difficulty of leaving behind childhood memories and dreams.