The Fourteenth Goldfish Series Books

Start with The Fourteenth Goldfish, then read its sequel, The Third Mushroom. The second story continues Ellie's life with her grandfather and builds on the first book's experiment with reversing age.

Sources: Penguin Random House's official first-book page, Penguin Random House's official sequel page.

The books discuss aging, immortality, illness, death, and the ethics of scientific discoveries in a warm, humorous way. A family pet becomes seriously ill, and experiments involving animals and a formula that changes a grandfather into a teenager may prompt questions from sensitive readers.

Middle-school friendship changes and a mild crush add everyday stakes. The strongest themes are curiosity, responsible science, accepting change, and recognizing that even exciting discoveries can have consequences.