Ruth is the thirteen-year-old daughter of Joseph and Margrit. Following her parents' sudden arrest, she immediately assumes an adult caregiving role for her younger siblings in war-torn Warsaw. She organizes their survival in a bombed-out cellar and starts a makeshift school for local displaced children. Driven by a fierce dedication to her family, she formulates the plan to travel to Switzerland and demands supplies from occupying soldiers to make the journey possible.

Edek is an eleven-year-old boy who uses his resourcefulness to keep his sisters alive in ruined Warsaw. He scales bombed-out buildings to salvage floorboards for beds and routinely smuggles food from the occupying forces. His dangerous activities and involvement with the Polish resistance place him at constant risk of arrest and forced labor. Despite contracting tuberculosis in a labor camp, he insists on continuing the journey to Switzerland.

Bronia is the youngest member of the family, separated from her parents during her early developmental years. She adapts to sleeping in freezing cellars and forests under her older sister's protection. She processes the violence and destruction around her by constantly drawing pictures of soldiers, destroyed buildings, and soup kitchen lines.

Jan is an orphaned pickpocket wandering the ruins of Warsaw with a small wooden box of possessions. Hardened by the loss of his parents, he deeply distrusts adults and places his faith entirely in his animal companions. A chance encounter leaves him carrying a silver sword letter opener, making him a crucial link for the scattered family as they attempt to reunite.

Joseph is a Polish primary school headmaster arrested as a political prisoner by the occupying forces. He endures freezing conditions and severe malnourishment at Zakyna camp, keeping himself sane by staring at tattered photos of his family. He escapes using a handmade boot-elastic slingshot and a stolen uniform, beginning a grueling trek back to Warsaw to search for his wife and children.

Margrit is Joseph's Swiss wife and the mother of Ruth, Edek, and Bronia. Her arrest and deportation to Germany as part of a forced labor program scatters her family and leaves her children to fend for themselves in the ruins. She is the original owner of the silver sword letter opener.

Ivan is a sentry working for a Russian lieutenant in Warsaw during the city's occupation. Though initially attacked by a defensive Jan, he proves to be a helpful contact for the children, providing them with crucial information about Edek's location at a transit camp and supplying them with shoes for their journey.

Jimpy is Jan's pet rooster and constant companion during the early stages of their survival in Warsaw. He represents Jan's strong attachment to animals over human beings in the wake of losing his parents.

Mark is a British officer stationed in post-war Berlin. He is impressed by Jan's ability to handle wild animals, specifically an escaped chimpanzee, and invites the traveling children into his home for dinner to reward them.

Bistro is a chimpanzee who escapes into the ruins of Berlin following Allied bombings. He forms a quick bond with Jan, who manages to calm the animal by offering it a cigarette.

Captain Greenwood is an American official handling military police duties in Germany. He oversees the investigation into an attempted train robbery, questioning Jan about his background and involvement with local thieves.

Kurt is a German farmer who, alongside his wife, offers the children food and shelter in exchange for farm labor. Having lost two sons in the war, he grapples with the conflicting emotions of housing Polish refugees while local authorities actively attempt to deport them.

Frau Wolff is a kind German farm wife who mourns the loss of her sons, Hans and Rudolf, who died fighting for the German army. She provides the traveling children with essential provisions and warmth during a critical leg of their journey, challenging Jan's preconceived hatred of all Germans.

Ludwig is the Wolff family's dog. He develops an intense, immediate attachment to Jan, complicating the children's desperate attempts to travel unnoticed when he secretly stows away in their canoe.

The Burgomaster is a local official tasked with executing American military orders to round up Polish refugees and send them back to Poland on lorries. He poses a significant threat to the children's goal of reaching Switzerland, dismissing their story as a fabrication.

Joe is an American soldier of Polish descent driving a truck through Europe. He offers the exhausted children a crucial ride toward the Swiss border, playfully joking about having wild animals in the back of his vehicle.