Three years after the events of the first film, Lenny Feder has relocated his family back to his Connecticut hometown where he and his friends grew up.
In the film's opening in the Feder household, Lenny wakes up to find a wild deer standing next to his bed. Upon waking up, his wife Roxanne startles the deer, causing it to urinate all over their home. Eventually, Lenny is able to get the deer out of the house just in time to take his children 17 year-old Greg, 13 year-old Keith, and 9 year-old Becky to their last day of school. Roxanne brings up the idea of their family having another baby, but Lenny says their family is perfect as is, upsetting Roxanne.
At the Lamonsoff household, Eric Lamonsoff and his wife Sally are at odds with each other over how to raise their children- Sally believes in unwavering support while Eric prefers to be more practical with them. At the McKenzie household, Kurt surprises his wife Deanne with a thoughtful anniversary present, only to find that she has completely forgotten. Meanwhile, Marcus Higgins is waiting at a train station after receiving a letter from an old girlfriend, who tells him that he has a seventeen-year-old son Braden. Marcus is stunned to see a tattooed, six-foot-tall boy, who turns out to be Braden. Marcus tries to be nice and takes him to school, but Braden shows an immediate dislike toward him.
After dropping off their kids, Lenny, Eric, Kurt, and Marcus spend the day roaming around town, reminiscing about the amazing summers they used to have when they were kids and Lenny's childhood bully, Tommy Cavanaugh. Lenny argues that he could take Tommy as a kid and he can still take him. Eventually, the friends go to see Becky's ballet recital, where Lenny runs into Tommy, whom Lenny is visibly terrified of. Tommy threatens that if Lenny ever lies again about being able to beat him up, he'll publicly beat Lenny up.
Once the kids are out of school, Lenny, Eric, Kurt, and Marcus decide to visit the old quarry, where they used to swim as kids. There they run into a bunch of partying frat boys who force them to jump into the quarry naked. Braden who was partying with the frat boys, witnesses this and goes off to vandalize their frat house. When the frat boys return, they swear to take revenge.
Lenny arrives home to help Roxanne set up for a 1980s-themed party for their friends. Meanwhile, Marcus begins to bond with Braden, who realizes he was wrong about his father. As all of their friends begin to arrive, Roxanne urges Lenny to consider having another baby. Lenny continues to protest the idea and is left dumbfounded when Roxanne reveals that she is pregnant. Lenny, feeling overwhelmed by this discovery, goes off to drink with his friends. The Feder's party goes well most of the night until Tommy Cavanaugh shows up and disrespects Lenny in front of everyone, so Lenny challenges Tommy to a fight. In a surprising turn, Tommy decides to take a dive so that Lenny can look tough for his kids, and the two develop a mutual respect. Soon after, the angry frat boys arrive at the house looking for retribution for the damage to their frat house. They go on to insult the local town residents, inciting a fight. The locals hold their own against the frat boys and eventually send them running away defeated.
After all the commotion dies down, the four friends have pancakes at Eric's mom's house. Mrs. Lamonsoff reassures Lenny that a new baby is a wonderful thing and eventually he will never be able to imagine life with just three kids. Lenny has a change of heart and returns home, telling Roxanne he is sorry and excited about the new baby, and they reconcile.
- Adam Sandler as Leonard "Lenny" Feder
- Kevin James as Erickson "Erick" Lamonsoff
- Chris Rock as Kurtis "Kurt" McKenzie
- David Spade as Marcus "Higgy" Higgins
- Nick Swardson as Nicholas "Nick" Hilliard
- Stone Cold Steve Austin as Dennis Cavanaugh
- Salma Hayek as Roxanne "Roxie" Chase-Feder
- Steve Buscemi as Wiley
- Jackie Sandler as Jackie Tardio
- Aly Michalka as Bikini Girl Savannah
- Maria Bello as Sally Lamonsoff
- Maya Rudolph as Deanne McKenzie
- Andy Samberg as Male Cheerleader
- Jake Goldberg as Greg Feder, age 17
- Cameron Boyce as Keithie Feder, age 13
- Alexys Nycole Sanchez as Becky Feder, age 9
- Ada-Nicole Sanger as Donna Lamonsoff, age 13
- Frank Gingerich as Bean Lamonsoff, age 9
- Nadji Jeter as Andre McKenzie, age 17
- China Anne McClain as Charlotte McKenzie, age 13
- Kaleo Elem as Ronnie McKenzie, age 4
- Di Quon as Rita
- Ebony Jo-Ann as Mama Ronzoni McKenzie
- Taylor Lautner as Frat Boy Andy
- Milo Ventimiglia as Frat Boy Milo
- Patrick Schwarzenegger as Frat Boy Cooper
- David Henrie as Frat Boy Zac
- Alexander Ludwig as Braden, age 17
- Allen Covert as Hippie Teacher
- Erin Heatherton as Female Cheerleader
- Taran Killam as Male Cheerleader
- Halston Sage as Nancy Arbuckle
- Cheri Oteri as Penny
- Ellen Cleghorne as Mary Fluzoo
- Shaquille O'Neal as Officer Fluzoo
- Chris Hardwick as Ice Cream Vendor