Blue Lagoon

The Blue Lagoon is a romance novel by Henry De Vere Stacpoole, first published in 1908 and it became an instant success.
Two young children are the survivors of a shipwreck in the South Pacific. After days afloat, they arrive and are stranded on a lush tropical island.
Together, cousins Richard and Emmeline Lestrange have to survive solely on their resourcefulness, and the bounty of their remote paradise. Years pass and both Richard and Emmeline grow into tall, strong and beautiful young adults. They live in a hut and spend their days fishing, swimming, diving for pearls, and exploring the island. During this period, they get along unthinkingly, although Richard often ignores Emmeline or takes her for granted, unless he needs an audience for one of his stories. Eventually, strange emotions start influencing their relationship.
Richard and Emmeline begin to fall in love, although they do not realize it. They are physically attracted to each other, but don't realize it or know how to express it.