Jinny is a 12- or 13-year-old girl who becomes the island's new Elder when her best friend departs. She loves her island home and cares deeply for her friends, especially her designated toddler, Ess. She struggles to balance her personal desires with her new leadership responsibilities, often avoiding difficult tasks like teaching swimming or reading. Jinny acts as a maternal figure to Ess while questioning the mysterious traditions that govern their isolated community.

Ess is a three- or four-year-old girl who becomes the island's youngest resident. She shares a cabin with Jinny, who serves as her guardian and primary teacher. Curious and generally cooperative, Ess enthusiastically learns simple island chores like making beds. She keeps a bracelet fashioned from her old shoelaces to comfort her when she misses her past life.

Deen is Jinny's best friend and the outgoing Elder of the island. He accepts the island's traditions without resistance, believing that his time to leave has naturally arrived. Before his departure, he imparts lessons to Jinny to prepare her for leadership, representing the inevitable progression of growing up.

Ben is the second-oldest child on the island, situated one year behind Jinny. He serves as the group's designated cook and acts as the Elder-in-training. Responsible and level-headed, he eagerly seeks instruction on how to lead the group and frequently steps in to manage chores or conflicts when others fail to do so.

Joon is an athletic and straightforward girl who ranks as the third-oldest child. She approaches island life rationally and rarely lets emotions cloud her judgment. Her physical agility makes her an excellent leader for supply runs, and she readily teaches younger children crucial survival skills when their designated guardians struggle.

Eevie is a younger girl on the island who struggles to accept her situation happily. She possesses sharp intelligence but channels her confusion and discontent into rude or defiant comments. Her negative demeanor frequently causes friction with the older children, particularly when she questions their decisions.

Sam is a young boy who was the youngest child until Ess arrived. He maintains a quiet demeanor and a cooperative attitude toward island chores. Having lost his protector, Deen, he learns to form new bonds with the other younger children and adapt to the shifting social dynamics.

Loo is an energetic and mischievous boy who brings disruption to the island routine. As a new arrival, he refuses to eat standard meals and frequently makes messes. His rebellious attitude complicates the established living arrangements and forces the older children to manage a toddler who actively resists their peaceful traditions.

Abbie Ellis is a former island resident from an unspecified time in the past. She left behind notes in the margins of the community's books, acting as a phantom friend to the current children. Her written legacy provides the group with humor, while a hidden letter she left behind introduces troubling questions about the outside world.

Oz is an athletic boy who spends most of his time with his best friend, Jak. The two boys look almost identical despite a two-year age gap. He contributes to the group by catching and cleaning fish, bringing energy and playfulness to daily island tasks.

Jak is a young boy who closely resembles his older friend Oz. He shares Oz's enthusiasm for fishing and roughhousing around the island. Together, they provide food for the group while occasionally causing minor disturbances with their boisterous games.

Nat is a quiet younger girl who helps with tasks like shucking oysters. She possesses a remarkable, albeit rarely used, talent for drawing. When the children acquire octopus ink, she produces a highly detailed and realistic portrait from her imagination, surprising the rest of the group.