Harriet is a 24-year-old woman working in sales who values traditional domesticity. She holds conservative views that clash with the progressive 1960s culture around her. Her desire to create an idyllic home with many children drives her early marriage.

David is a 30-year-old architect seeking a wife who shares his old-fashioned values. Coming from a divorced household, he is determined to build a stable, traditional family home. He holds onto an image of himself as a protector and provider.

Ben is the fifth child of Harriet and David Lovatt. From birth, he displays unusual physical traits, immense strength, and a lack of standard social engagement. His presence immediately disrupts the family's established domestic routine and expectations.

Dorothy is Harriet's widowed mother who provides practical childcare and household assistance. She offers a pragmatic perspective on motherhood that contrasts with her daughter's boundless idealism. She establishes clear boundaries regarding how much of herself she will sacrifice.

Luke is the eldest Lovatt child. He is an easygoing boy with fair hair and blue eyes who conforms exactly to his parents' vision of a perfect family.

Helen is Harriet and David's second child. Like her older brother, she is described as cherubic and easy to raise, fitting seamlessly into the household.

Jane is the third child in the Lovatt family. Her arrival continues to validate her parents' belief in their ability to manage a large, happy home.

Paul is Harriet and David's fourth child. He requires more attention than his older siblings, and his infancy is quickly overshadowed by Harriet's unexpected fifth pregnancy.

Molly is David's mother and an academic who holds upper-middle-class views. She is openly critical of Harriet and David's intention to have a massively large family.

Frederick is David's stepfather and a fellow academic. He shares his wife's skepticism regarding the Lovatts' domestic plans and finances.

James is David's wealthy, jet-setting father who builds luxury yachts. Though critical of his son's choices, he provides the essential financial backing that allows the Lovatts to maintain their lifestyle.

Jessica is James's younger, wealthy wife. She possesses a worldly attitude and happily finances the Lovatts' domestic project from afar without personal involvement.

Dr. Brett is Harriet's obstetrician. He consistently dismisses Harriet's concerns about her pregnancy and views her intense pain as an exaggeration.

Sarah is Harriet's sister who remains in an unhappy marriage. The birth of her daughter Amy provides Harriet with a point of comparison for her own family's supposed perfection.

William is Sarah's husband who struggles with unemployment, causing strain in their marriage.

Amy is Harriet's niece, born with Down syndrome. Harriet unfairly uses Amy's condition to validate her own superstitious beliefs about family happiness.

Alice is Frederick's older cousin. She provides temporary domestic help to the Lovatts but is deeply unsettled by the household's atmosphere after Ben's arrival.

Bridget is David's 15-year-old cousin. She initially admires Harriet's life but becomes quickly disillusioned when the reality of the Lovatts' situation becomes apparent.

Angela is another of Harriet's sisters. She is outspoken and willing to accuse the Lovatt family of callousness when they discuss institutionalizing Ben.

Mrs. Graves is a school headmistress. She handles difficult students by applying standard labels like 'hyperactive' rather than addressing their specific underlying issues.

Dr. Gilly is a medical specialist who evaluates Ben. She attributes the household's problems to Harriet's maternal failings rather than acknowledging Ben's distinct differences.

John is a shaggy, good-natured youth who works in the overgrown garden. He treats Ben with straightforward firmness and becomes the first person outside the family to connect with the child.

Derek is one of the older, alienated schoolboys who befriends Ben. He is part of an unemployed youth group that rejects mainstream social expectations.

Billy is a member of the truant group of older boys at Ben's school. He spends his time occupying the Lovatts' empty rooms.

Elvis belongs to the group of socially excluded youths who take an interest in Ben and regularly gather at his house.

Vic is part of the hostile tribe of schoolboys who form a makeshift community around Ben.