The Blue Lagoon

The Blue Lagoon is a 1908 novel by Henry De Vere Stacpoole. There are two sequels, The Garden of God, published in 1923 and The Gates of Morning, published in 1925.

The novel is about two young cousins, Richard and Emmeline Lestrange, and galley cook Paddy Button who are marooned on a tropical island after escaping their burning ship. Paddy teaches the kids how to survive on the island, before dying in a drunken haze, leaving the two to fend for themselves.

There have been three film adaptions. A 1923 silent film directed by W. Bowden and Dick Cruickshanks. A 1949 version directed by Frank Launder. The 1980 adaption directed by Randal Kleiser and starring Brooke Shields and Christopher Atkins. In 1991, William A. Graham produced and directed a loose adaption of The Garden of God titled Return To The Blue Lagoon starring Milla Jovovich and Brian Krause.

All three novels are online here under "E-texts". Serious scholars of Edgar Rice Burroughs' work believe they can track part of his inspiration for Tarzan to these novels and to Morgan Robertson's earlier novella, Primordial.

Tropes used in The Blue Lagoon include:

Caught with Your Pants Down: In the film there's a scene where the boy, seen from behind, is clearly masturbating. The girl asks him "What are you doing?" and he guiltily says "Nothing!"
Children Are Innocent
Coming of Age Story
Convenient Coma: In the novel, Emmeline comes walking out of the forest with the baby she had a few hours earlier. She explains to Richard that she felt ill, went to sit in the forest, and then "remembered nothing more" until she woke to find the little creature lying beside her. Apparently she remembers more about the birth later.
Deserted Island: Take a wild guess...
Diabolus Ex Machina: In a movie based primarily around emotional and physical self-discovery, Diabolus is personified in the form of a three-year-old boy throwing oars from boats.
Eighties Hair: Despite being stranded on an island since childhood, Richard somehow manages to have a consistent perm.
The Film of the Book
Godiva Hair: Emmeline. To the point (as pointed out by Roger Ebert) of Narm.
Kissing Cousins: Richard and Emmeline are cousins. They are also the only available mates for each other.
Loin Cloth
Mighty Whitey: Dick Lestrange, son of the original couple. He appears in the sequel, The Garden of God and the followup novel The Gates of Morning. He can best be described as an intelligent, likeable and very easygoing Surfer Dude. Katafa, something between a Jungle Princess and a Broken Bird, washes up on the shore and causes trouble. She isn't really a Kanaka, but a Spanish girl who was Raised by Natives. To ensure the plotline, she's been cursed as an untouchable. After sundry how-likely-is-that events, Dick and Katafa fall in love. Katafa becomes touchably soft and takes him home with her, where he is immediately hailed as King, the old King having died in Katafa's absence. More to the point, laid-back ol' Dick immediately accepts, as a matter of course! (Having earlier picked up a Royal MacGuffin probably helped with this decision.) Stacpoole (usually fairly nonracist) clearly implies that in their present predicament, the natives need a white couple to save them.
Noble Savage: Richard and Emmeline in the original film, and Richard (son of the couple from the first movie) and Lilli of the sequel. They pretty much raise themselves to adulthood and know little of human civilization. On the other hand, the original inhabitants of the island are seen practicing human sacrifice. Nothing particularly noble about them.
Nostalgic Music Box: Among the artifacts taken to the island is a music box that plays Chopin's Nocturne Op. 9, #2 in E flat major. Emmeline says "That's Chopin! I can play it on the piano." It's used by the kids growing up as a connection with/nostalgic reminder of their life before the island. Sometimes they dance to it. None of this is in the book.
Robinsonade
Scenery Porn: It even got an Academy Award nomination for its cinematography.
Walking Shirtless Scene