Based on the real life Gilbreth family. The name Gilbreth appears several times throughout the film: Nora says that it's her grandmother's name when the kids are playing the game with the apples; it's Kate's maiden name according to her yearbook; it's Kate's maiden name according to the dust jacket of her book.
The real family had 6 boys and 6 girls.
The actual family did not have any twins. All the children were single births and the father regretted this because he felt multiple births to be more efficient.
Director Cameo: [Shawn Levy] the reporter who asks Tom for a quote.
When Hank (Ashton Kutcher) gestures to his face ("This is the moneymaker!"), the motion he makes is the American Sign Language sign for "beautiful".
The part where the twins dump the whole entire bag of dog food wasn't in the script - the twins made it up.
Steve Martin and Bonnie Hunt, playing the parents of 12 children, have zero children between them in real life.
Chloe Greenfield unsuccessfully auditioned for the part of one of the fraternal twins.
The names of the kids from oldest to youngest are Nora, Charlie, Loraine, Henry, Sarah, Jake, Mark, Jessica, Kim, Mike, Nigel, and Kyle.
At the beginning of the movie, Kate reveals the title of her new book to be "Cheaper By The Dozen". Although this movie is loosely based on a book by that title about a real-life family, the book was written by one of the sons, Frank B. Gilbreth Jr., along with his sister, Ernestine Gilbreth Carey. Although this film is based on that same book that inspired the 1950 film (Cheaper by the Dozen (1950)), the only element it retains from the original is the idea of there being 12 children in one family. Even the names of the characters are changed.
Steve Martin is a huge fan of the "Doctor Who" series, and playing a character named "Tom Baker" is the closest he'll ever get to accomplishing the goal of so many Doctor Who fans: playing The Doctor, a character who for seven years was played by actor Tom Baker.