Other mistake: At the beginning of the film, Lorraine is in the bathroom while her sister is banging on the door outside. Notice how blonde her hair is as she is applying her lip gloss. At the breakfast table a few minutes later her hair is a different type of blonde. This is because Hilary Duff wasn't available at the time of filming the beginning of the movie and her bathroom sequence had to be filmed many months after the filming for the rest of the film had been completed.
Other mistake: When Steve Martin is seated at the table trying to find a babysitter, there are several quick shots of the phone book as he crosses out numbers, turns the page, etc. The very last shot of the phone book is backwards! While its easy to see the phone book, if you zoom in on the shot, you can clearly see that the tiles, words and letters on the board partially obscured by the phone book are backwards too.
Continuity mistake: When the kids are about to put Hank's underwear in the meat bucket, Henry and Jake insert cotton-ball type things in their noses. After they do this, we see that there is still a good amount of white sticking out, but in the very next shot, there is barely any white showing.
Continuity mistake: At school Mike Baker knocks the latte out of the bullys hand, and the latte falls to the floor spilling a bit of drink on the bullys shoe. Yet in the next wideshot of Mike lunging at the bullys legs, the drink cup has vanished and both of the bullys shoes are clean.
Continuity mistake: At the beginning of the movie, Steve Martin comes into their bedroom after a jog where his wife is proofing her manuscript. There's a pinwheel type of decoration attached to the lamp on top of some family photos in the corner by the window. In the 1st shots, you can even see its shadow on the lamp. Steve says (to Bonnie Hunt) "We could use a little change around here - like this lumpy old mattress." He then moves to the mattress facing her and the photos are still there but the pinwheel thingy is gone.
Continuity mistake: In the kitchen when Kyle and Nigel run to their dad, Tom, and start yelling and doing macho actions, in a wideshot you see Charlie walk from the stove, over to the worktop where Henry, Kim and Jessica are making sandwiches and he puts something on a shelf. Then in the following closeup of Nigel and Kyle you can see in the background that he has instantly vanished.