The Water-Babies by Charles Kingsley

The Water-Babies, A Fairy Tale for a Land Baby is a children's novel by the Reverend Charles Kingsley. Written in 1862-1863 as a serial for Macmillan's Magazine, it was first published in its entirety in 1863. The book was extremely popular during its day, and was a mainstay of children's literature through the 1920s.
The protagonist is Tom, a young chimney sweep, who falls into a river after encountering an upper-class girl named Ellie and being chased out of her house. There he dies and is transformed into a "water baby", as he is told by a caddis fly — an insect that sheds its skin — and begins his moral education. The story is thematically concerned with Christian redemption, though Kingsley also uses the book to argue that England treats its poor badly, and to question child labour, among other themes.
Source: Wikipedia