Big Daddy

In New York City, Sonny Koufax is a 32-year-old slacker and law school graduate who hasn't taken the bar exam, works one day a week as a toll booth attendant, and lives off a $200,000 compensation from a minor accident. His girlfriend Vanessa threatens to break up with him unless he takes more responsibility. His roommate Kevin Gerrity proposes to his podiatrist girlfriend Corinne Maloney before he leaves for China to work on a case for his law firm, and she accepts. Corinne vehemently dislikes Sonny, including him constantly teasing her about her former job at Hooters.

The next day, Sonny wakes up to find Julian McGrath, a five-year-old left at their apartment. A note states that his mother is no longer able to care for him and that Kevin is his biological father. Sonny contacts Kevin, who is puzzled by the news. Despite his selfishness and lack of parenting skills, Sonny assures him that he will take care of Julian until Kevin returns from China. To win Vanessa back, Sonny introduces her to Julian. However, he discovers that she is now dating Sid, an elderly man whom, despite being 36 years her senior, she reveres as more motivated and intelligent, with a "five-year plan".

Posing as Kevin, Sonny takes Julian to his social worker Arthur Brooks, telling him that Julian should return to his mother. However, Brooks informs Sonny that Julian's mother died of cancer. Sonny then decides to raise Julian his own way. They develop a strong bond, and Julian helps Sonny find a new girlfriend in Corinne's lawyer sister Layla. Brooks finds a foster home for Julian and leaves messages for Sonny, but is suspicious when he does not respond.

At a meeting at Julian's school, Sonny rethinks his parenting methods after Julian's teacher complains about the habits he has developed due to Sonny's influence. He turns Julian's behavior around, but then Brooks arrives to find out Sonny impersonated Kevin, and threatens to arrest him if he does not hand over Julian. Sonny complies but contacts Layla to help take legal action.

In court, numerous people, including Corinne, testify on Sonny's behalf and tell the judge he is a good father. Julian also testifies and provides information regarding his heritage. Sonny then calls himself to the stand and asks his lawyer father Lenny, visiting from Florida, to question him. Despite Lenny's fervent belief that he is not father material, Sonny convinces him that he will not fail at being a father. Impressed by Sonny's sincerity, Lenny vouches for him. Nonetheless, the unconvinced judge orders Sonny's arrest. Kevin, realizing he truly is Julian's biological father, refuses to press charges against Sonny. Kevin is granted custody of Julian, and Sonny promises him that he will always be there for him. He then passes Julian to Kevin, and they start to bond.