Liam is a 12-year-old boy who is unusually tall and sprouts facial hair, causing adults to mistake him for a grown man. He enjoys playing World of Warcraft, an environment where his height does not matter. Following an exhilarating experience on a fairground ride called the Cosmic, Liam seeks more thrills. He poses as an adult to enter a secret competition, traveling to a remote facility in China.

Florida is a student in Liam's drama club who agrees to pretend to be his daughter for the Drax contest. She desires celebrity status, secretly hoping that gaining public attention will encourage her absent father to return. She brings a focus on superficial glamour to the trip but slowly shows interest in the scientific principles behind their physical training.

Dr. Drax is the eccentric and highly enthusiastic owner of the Drax Corporation. Having inherited the company from her father at age 12, she orchestrates a secretive competition in the Gobi Desert, inviting fathers and children to test a new invention. She displays a visionary attitude but refuses to acknowledge genuine safety risks.

Liam's father is a taxi driver with a dry sense of humor who serves as Liam's primary role model. He provides stability and gentle authority, appearing precisely when Liam needs him most during early misadventures. Liam studies his behavior to mimic the demeanor of an adult father.

Liam's caring mother worries deeply about her son growing up too fast. She takes him to doctors to investigate his sudden physical maturation, representing the natural parental fear of a child advancing into adulthood prematurely.

Mr. Xanadu is a wealthy, highly materialistic father participating in the Drax contest. Because of trauma during a war, he views the world strictly through a financial lens, believing everything and everyone has a price. He attempts to buy advantages and votes during the competition, carrying ice cream into the desert to bribe others.

Hasan is the anxious son of Mr. Xanadu. He inherits his father's obsessive focus on money and survival, acting more like a stressed adult than a carefree child during the contest. He carries lingering fears from a near-kidnapping experience during a war.

Monsieur Martinet is an intensely competitive father from France. He places extreme pressure on his son to succeed, often relying on anger rather than encouragement to motivate performance during the physical challenges.

Max is the son of Monsieur Martinet. Under his father's harsh expectations, he develops an obsession with winning and struggles to accept failure or participate in activities purely for fun. He views every task as a high-stakes test of his worth.

Samson One is an intellectual, deeply logical father who prioritizes reason over emotion. He maintains a detached demeanor during the high-stakes contest, failing to provide emotional comfort to his son during frightening tasks.

Samson Two is the highly intelligent son of Samson One. He copes with fear and anxiety by retreating into logic and mathematics, frequently trying to convince himself that the terrifying situations they face are merely simulations.

Mr. Bean is an employee at the Drax compound in China who interacts with Liam. He is an experienced astronaut who offers severe warnings about the psychological effects of space travel and advises Liam to pack items that connect him to home.

The Headmistress is the principal at Waterloo High. Due to Liam's height and stubble, she mistakes him for a newly hired staff member on his first day, introducing him to the entire school during an assembly before realizing her error.