Martha Plimpton plays the older sister of Joaquin Phoenix a.k.a. Leaf Phoenix. In real life, she dated his older brother River Phoenix for nearly five years. River Phoenix and Plimpton also appeared in two movies together.
In this film, Steve Martin plays the father of several children. In reality, Steve Martin did not become a parent until he was 67 years old, in 2012.
According to Ron Howard in an interview, the scene where Helen discovers the nude pictures was actually an incident that happened to producer Brian Grazer.
During filming, the cast became obsessed with playing the murder game (a game in which one person, who is the murderer, has to find a subtle way to kill other players simply by looking at them without giving themselves away as the murder). This is very apparent in the dinner scene where everyone is sitting around the table. If you watch everyone's eye movements, it's obvious they are playing the game.
This movie is based on Ron Howard, Brian Grazer, Lowell Ganz, and Babaloo Mandel's experiences as parents.