Gil Buckman (Steve Martin), a neurotic sales executive, is trying to balance a family in suburban St. Louis and his career. He wants to be an active father, rather than the distant workaholic that his own father was. When he finds out that his eldest son, Kevin, has emotional problems and in the opinion of the school psychologist needs therapy, and also that his two younger children, daughter Taylor and youngest son Justin, both have minor issues as well, he begins to blame himself and deeply question his abilities as a father. In addition his wife, Karen (Mary Steenburgen), becomes pregnant with their fourth child, which he is unsure he can handle.He is frustrated and fearful that the financial burdens of another child and office politics at work, which include a manager who is blatantly dishonest and manipulative, are turning him into the detached workaholic he despised his own father, Frank (Jason Robards), for being. This comes to a head near the end of the film, when Frank comes to Gil for advice on how to deal with Larry (Tom Hulce), Gil's younger wayward brother, and says bluntly that he is asking Gil's advice because he knows Gil always thought he was a lousy father and because he also knows that Gil is a good father. Gil, who has been humbled by his children's issues and his own issues at work, opens up about his self doubts as a parent. Frank tries to reassure him in a casual way by telling him that he worries too much, and the two have a reconciliation of sorts with Frank telling Gil that worry for one's child never ends.Throughout the movie, Gil tries to lighten up more and be less fearful of the surprises he encounters in life and this has a good effect on Kevin, whose emotional problems begin to recede. When a hired cowboy character fails to show up at their birthday party, Gil dresses as a cowboy himself and assumes the role.His sister, Helen (Dianne Wiest), is a divorced bank manager and her dentist ex-husband wants nothing to do with their children, Garry and Julie. He has a new wife and young son to whom he is very devoted. At first, Garry (Joaquin Phoenix), who has just entered puberty, appears to be a very disturbed boy. He is quiet, not involved, and likes to be alone in his room with a mysterious paper bag. At first Helen worries that the bag contains drugs or alcohol, but the bag was actually filled with porn that he would masturbate to in his room.Helen's daughter, Julie (Martha Plimpton), is still in high school, but doesn't seem interested in school or her future even though she got 1300 on her SATs. She is already having sex with her slacker boyfriend, Tod Higgins (Keanu Reeves), and the two of them want to start their lives together. They get married, Julie gets pregnant, and the two live at her mother's house. When in desperation Helen asks Tod to talk with Garry, Tod is able to form a strong bond with him by reassuring him that his obsession with girls and sex is not perverted, but normal for a boy his age. This is a tremendous relief to Garry, and he becomes much happier.This also greatly increases Helen's respect for Tod and she forms a strong bond with him too. She is relieved when Tod tells her what was really bothering Garry all along. Tod also mentions that she at least isn't abusive like his father was. Eventually she supports Tod and respects his and her daughter's relationship to the extent that when Julie wants to break up with him because of her fears with his profession (drag racing) Helen orders her to face her fears and support him also, even when he has a racing accident. She ultimately marries Garry's biology teacher who becomes the loving father figure that Garry in particular was so desperate to have.Gil's other sister, Susan (Harley Kozak), is a middle school science teacher married to an intelligent but slightly neurotic scientist husband, Nathan Huffner (Rick Moranis). They have a sweet, precocious daughter, Patty. Susan wants more children, but Nathan is overly obsessed with their daughter's cognitive development and as a result, Patty is unable to relate to other children and Susan is neglected by all the attention that Nathan focuses on Patty, to the point of including Patty on a romantic getaway that Susan planned for just the both of them. Susan lashes out by eating junk food hidden in the closet and by compromising her diaphragm as a plan to get pregnant despite her husband's wishes. She eventually gets so frustrated with the situation that she leaves her family, causing Susan to struggle with her work and Nathan to eventually drop by one of her classes unexpectedly, serenading her in an effort to win her back. He promises Susan he will try to change and will lighten up about Patty, and Susan agrees to move back into their home.Finally there is Larry (Tom Hulce), who, rather than settle into a career, has drifted through life trying to cash in on get-rich-quick schemes. Though he is the black sheep of the family, he is Frank's favorite (mainly because he reminds him of himself at a younger age). He has recently shown up, along with his bi-racial son, Cool (who was the result of a brief affair with a Las Vegas showgirl), and wants to borrow money from his father, supposedly for another of his get-rich-quick schemes. As always, Frank is supportive.But soon it becomes apparent that Larry has a gambling problem and needs the money to pay off his extensive gambling debts, $26,000, or else he must pay with his life. Frank is disillusioned about Larry, but still loves him and tries to help. Frank refuses to bail him out completely, but offers to teach him the family business (plumbing supplies) so he can take it over from Frank (who has to put off retirement) and use the income to pay off the gambling debts. Larry "adds a wrinkle" which involves going to Chile, and Frank recognizes that his son will never stop wasting his life. He agrees to look after Cool and when his grandson asks if Larry is coming back, Frank says no, then asks if he'd like to stay with them. It is implied that Larry will disappear, with the irate criminals he owes money to on his tail; he is not seen again.The film ends on a sentimental note with a new generation of Buckman children being born and the personal growth of the parents. Helen has just given birth to a baby girl, which is the reason why the family is reunited at the hospital. Frank lovingly hugs and cuddles his grandson, Cool, demonstrating that he changed his distant ways. Tod and Julie remain together (despite Helen's less than sunny predictions for their chances), raising their son. Nathan has lightened up as a parent. Susan is visibly pregnant. Gil and Karen are now the proud parents of four.