Tom arrives home to the delight of Mrs. Tulliver and Maggie, who dotes on Tom affectionately. Tom greets Maggie and shows her the fishing line he has saved all term to buy her, so that they can go fishing tomorrow. Tom had to fight some boys over his money, and Maggie adoringly compares his strength to Samson's. Impatient with Maggie's hypothetical imaginings, Tom decides to go see his rabbits, and Maggie must confess that they are dead. Tom tells Maggie he doesn't love her and severely reminds her of her past naughtiness. Maggie, distraught, clings to Tom, but he shrugs her off. Maggie retreats to the attic and remains there, miserable, until her presence is missed at teatime. Mr. Tulliver, suspecting that Tom has been hard on her, orders Tom to fetch her and treat her kindly. Maggie begs Tom's forgiveness, and the two share the cake that Tom has brought and nuzzle each other like "two friendly ponies."
Tom and Maggie go fishing the next day. Maggie is respectful of Tom's practical knowledge of the outdoors and is impressed by his superiority and refusal to acknowledge her bookish cleverness. Maggie, through no skill of her own, catches a fish. Today, both Tom and Maggie envision that they will always be together, and always be happy. The narrator informs us that their lives will change. But as the narrator him/herself strolls in the woods, he/she reflects that childhoods spent outdoors inspire a lifelong love of nature that affects one's perception of the world.
Mrs. Tulliver prepares for the visit of her sisters—all former Miss Dodsons—and their husbands and children. Though Mr. Tulliver scoffs at the opinions of the Dodsons, Mrs. Tulliver values their participation, not least because they each have money saved to be left to their nieces and nephews. Her sister Mrs. Deane will bring her daughter Lucy, whom Mrs. Tulliver loves as her own as a result of Lucy's demureness and coloring. The Dodsons consider themselves a respectable family with a sense of superiority and particular ways of maintaining households and social relations meant to distinguish themselves from other families.
Tom steals two pastries from the kitchen for himself and Maggie. Maggie offers to take the one with less jam, but Tom insists that she choose between them fairly, without looking. Maggie ends up with the bigger pastry, and Tom refuses when she tries to give it to him. But he finishes his own smaller one first and watches angrily as she eats all of her larger one, calling her "greedy." Tom runs off, and Maggie sits feeling regretful and confused about the pastry. She arouses herself finally to realize that Tom has gone off with Bob Jakin.
Tom and Bob play heads-or-tails with Bob's half-penny, and Bob cheats, snatching back the coin and claiming it was heads. Tom accuses Bob of not playing fair, and the two fight. Tom forces Bob to give him the half-penny, then refuses to take it, saying he doesn't play with cheaters and won't hang around Bob anymore. Bob yells insults after Tom and throws the pocketknife that Tom had given him, picking it up again when Tom is out of sight.
Mrs. Glegg is the first of the Dodsons to arrive at the Tullivers. All the Dodsons are handsome women, though Mrs. Glegg stingily keeps her new or expensive clothing in storage, wearing shabbier clothing that smells of mold instead. Mrs. Glegg reproaches Mrs. Tulliver for various extravagances while they wait for the others to arrive. The Pullets soon come; Mrs. Pullet is crying dramatically over the death of an acquaintance. Mrs. Pullet goes with Mrs. Tulliver to admire a new hat, while Mrs. Glegg ruminates on their extravagance and on the unbecoming qualities of Maggie, who resembles her father's sister, Mrs. Moss, rather than the Dodsons.
The Deanes arrive, and Maggie and Tom come in to greet Lucy Deane. Mrs. Glegg speaks loudly to Mrs. Tulliver of the need to thin out Maggie's unruly hair. Maggie and Lucy get permission from Lucy's parents for Lucy to stay over. Maggie drags Tom upstairs with her to have him watch while she cuts her hair. Instead of joining in her rebellious triumph, Tom laughs and insults her new appearance. Tom goes downstairs, leaving Maggie feeling remorseful. First Kezia, the family servant, then Tom come upstairs and finally coax Maggie down to dinner. Everyone is shocked—then the women are reproachful and the men amused. Maggie begins to sob, and her father comforts her.
The children soon adjourn with their dessert, and Mr. Tulliver announces his plans for Tom's education. Mrs. Glegg in particular is skeptical and pessimistic about this plan. Mr. Tulliver and Mrs. Glegg quarrel, and Mrs. Glegg leaves, taking Mr. Glegg with her.
As the title of Book First, "Boy and Girl," suggests, much of these chapters are spent examining Maggie and Tom's childhood relationship. Eliot presents their relationship as close, with Maggie as dependent upon Tom. Imagery such as that used to describe Maggie's hugs—"Maggie hung on his neck in rather a strangling fashion"—lend an ominous tone to their relationship and foreshadow the final events of the novel. While Tom can be affectionate and loving toward Maggie, we also see that he does not encourage her cleverness, as her father does. Tom immediately cuts off Maggie's imaginings about Tom's hypothetical bravery when faced with a lion. Though Tom shares Maggie's fantasy of the two of them always living together happily, part of his fantasy involves exerting dominion over her by always "punish[ing] her when she did wrong."
Indeed, the depiction of Maggie and Tom's childhood relationship in Book First raises an important theme of forgiveness and justice. Tom is characterized as a stubborn boy who sticks to a code of fairness in his dealings and judgments of others. The administration of this code can cause pain to others, as with Maggie's confusion over proper conduct in the matter of the pastry in Chapter VI, or indirectly affect Tom adversely, as with the loss of Bob Jakin as a playmate. Yet, Tom always feels satisfied in the knowledge that he has acted correctly. Maggie, on the other hand, operates in relation to feelings. When she is deemed naughty by Tom or her mother or another, she does not reflect on the fairness or unfairness of the judgment against her but focuses instead on the misery of feeling unloved. Maggie craves forgiveness and offers forgiveness to others—she even inspires forgiveness in Tom in Chapter V through the overwhelming power of her own love and affection. The only twist on this is that Maggie does not easily forgive herself. Unlike Tom, who feels secure in his actions, "Maggie was always wishing she had done something different."
In her essay "Silly Novels by Lady Novelists" (1856), George Eliot disparaged several genres of novels, all of which violate realistic conventions by making their characters extraordinary beyond belief. One of the violations she focuses on is the tendency to sentimentalize child characters and put language in their mouths more befitting an adult. Eliot seeks to make Tom and Maggie seem realistic by focusing precisely on their immaturity. Through this, another theme of the section emerges—the lack of life perspective felt by children. Maggie's dramatic scenes of grief are connected repeatedly in the narrative to her inability to put her miseries in the context of past trials overcome or enjoy the experienced faith in the future.
The Tullivers and the Dodsons discuss Maggie's and Tom's physical and behavioral characteristics in relation to each of their parent's family line. This line of conversation, combined with the narrator's discussion of the faculties that distinguish humans from animals, reveal the historical context of Darwinism to George Eliot's novel. Darwin published his study On the Origin of the Species by Means of Natural Selection; or the Preservation of Favoured Races in the Struggle for Life in November 1859 as George Eliot was in the midst of writing The Mill on the Floss. Eliot was already interested and knowledgeable in the field of natural history and the language of natural history occurs throughout The Mill on the Floss.
The end of Chapter VII includes the main plot event of Book First—the quarrel between Mr. Tulliver and Mrs. Glegg. The quarrel will cause a dispute over the five hundred pounds lent to the Tullivers by Mrs. Glegg that will last for the rest of Book First. In the larger plot of the novel, this minor money issue will be the first in a series of events that lead to Mr. Tulliver's financial downfall.