The scene where Lulu tells Shane that she thinks he's cute and Shane's embarrassed response was based on a real life incident on set. Morgan York (the actress who plays Lulu), upon meeting Vin Diesel, actually said that to him and he awkwardly responded with a "thank you". The director thought it was so funny, that he put it in the film.
The idea of the family having a pet duck was introduced by Thomas Lennon and Robert Ben Garant when their script had Jackie Chan attached. The running joke was that Chan's plan to kill the duck and cook it for dinner horrified the kids, and therefore Chan ended up reluctantly keeping and taking care of the pet. Even when Chan exited the project and other writers worked on the script, the duck stayed all the way through to the finished film.
The play at the end of the movie was shot in a local (Toronto) professional theater called Theatre Passe Murielle. Over four days, many scenes from The Sound of Music (1965) were shot, including "Do, Re, Mi", "My Favorite Things" and "The Lonely Goatherder". These scenes were fully staged, choreographed and costumed. Some of the costumes came from the original "Sound of Music" film. In the end, almost all of it ended up on the cutting room floor.