Swallows and Amazons

''Swallows and Amazons'' by Arthur Ransome, first published in 1930, public domain.
John, Susan, Titty and Roger sail their boat, Swallow, to a deserted island for a summer camping trip. Exploring and playing sailors is an adventure in itself but the island holds more excitement in store. Two fierce Amazon Pirates, Nancy and Peggy, challenge them to war and a summer of battles and alliances ensues.