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. (00:02:15)
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. (00:07:30)
Continuity mistake: At the kitchen table, Kate is throwing toast, and she throws one piece at Kim (the twin) who catchs it. Yet in the very next wideshot Kim is leaning on the table, with no toast in her hands, and Kate throws Kim another piece of toast again. (00:08:10)
Continuity mistake: When Beans the frog has been caught, Tom gives Mark the net with the frog in and then Mark smashes all of the glass/ornaments on the shelf, by swinging the handle of the net into them. Look at the mess of glass/ornaments on the side, just after Mark smashes them. When we see the shelf again, the position of the smashed glass/ornaments on the side had changed greatly, and things have appeared/disappeared. (00:09:45)
Continuity mistake: At the beginning during the breakfast scene, the eggs splatter all over everyone and some gets on Steve Martin's chin and you can see it fall off, they then show a shot of FedEx and then show Steve Martin again and the egg is back on his chin. (00:10:15)
Continuity mistake: As Tom is about to go to work, Kate hands him a printout of Nora's email. Tom takes the paper and holds it at the bottom middle part. In the following closeup though, Tom is holding the left corner of the paper. When it cuts he is holding the bottom middle again. (00:11:20)
Continuity mistake: When Nora phones the Bakers, and she is on speakerphone, in the background you can see some various blue and green glass ornaments on the red wall-side, in the background of Hank playing his video game. These ornaments have moved along in the closeup of Hank frantically tapping his controller. (00:16:00)
Continuity mistake: When everyone is walking to the new house, in the overhead shot you can see Tom and Kate walking with their arms around each others shoulders. Then when it cuts to a closeup, they are standing with their hands down by their sides. (00:20:55)
Continuity mistake: When the chandelier breaks and Tom falls whilst holding it, between shots the chandeliers lights go from being pretty much intact, to being totally smashed - and this is after the fall, so there is no reason for them to smash any more. The long yellow rope that attachs the chandelier to the ceiling changes the position it lays between the closeup of Tom landing (obviously not Steve Martin) and the following wideshot too. (00:24:25)
Continuity mistake: When the Baker's first move in and Dylan's family comes to visit, right after Dylan falls off of the Chandelier, Jake throws one of his shoes down (not both). In the next shot, the father is holding both shoes. (00:25:45)
Continuity mistake: When Tom is being interviewed on TV, it cuts to Lorraine who says "At least we get to see him on TV" and she has both her legs bent up in front of her. In the following wideshot of the 8 kids and Kate on the bed, Lorraine only has one leg bent up in front of her. (00:27:55)
Continuity mistake: When Nora is on the phone to the Bakers, trying to find a way not to visit them, she talks to Hank whilst covering the phone mouthpiece, and on the side are three blue candleholders, yet in some shots one of the candleholders disappears. (00:30:30)
Continuity mistake: As Hank falls into the paddling pool he clearly drops the apple he was holding into the pool, yet in the following closeup he has the apple in his right hand. (00:34:15)
Continuity mistake: When Sarah and Jake grab a handful of meat from the kitchen, Sarah is wearing purple and Jake is wearing red. Both are wearing different clothes a moment later when they are in the basement with Mike and Henry, soaking the underwear. (00:34:45)
Continuity mistake: When Hank is sitting on the couch, waiting for his clothes to dry, Nora comes in with lemonade. Tom and Kate start talking to Hank about his acting career and we see that Nora is holding her lemonade glass, but in the very next shot, the glass is on the table in front of her. (00:35:30)
Continuity mistake: When Hank is tripped by the hose, his hair goes from dry to suddenly wet just before he hits the water. (00:35:40)
Continuity mistake: When Gunner is running under the table towards Hank, on the left we can see Henry's and Jake's legs as if they are sitting at the table. But neither Henry or Jake are sitting at the table at this moment, we see them come into the room a few seconds later. (00:38:05)
Continuity mistake: When Hank is being attacked by the dog and the family is looking on and laughing, it cuts to Charlie laughing and he is holding a glass to take a drink, then it cuts back to Hank, and just a second later it cuts back to the family at the table and Charlie is sitting with his arm across his chair facing a completely different way, with nothing in his hands. There is no way he could have put down his glass and turned to lean back with his arm across the chair in that short of time. (00:40:20)
Continuity mistake: When Steve Martin is talking to Bonnie Hunt about being gone for three days, watch the picture on the table. It moves closer to the edge of the table in the subsequent shot. In the first shot it is not covering the ring on the edge of the table, in the next shot it is. (00:43:10)
Continuity mistake: After Mark has been bullied, we see the bullies walk away and do their handshake, but in the very next shot (from a different angle) they do their handshake again. (00:43:35)
Answer: It seems that the fact the family can't take care of themselves is added to part of the humour of the film. 12 children is a lot, and think about all those rows and all that mess.
Hamster ★
It's not like they couldn't take care of themselves. As shown with the breakfast scene at the beginning, they seem to function pretty well when they all get along. Tom and Kate were just usually home more frequently than some other parents. It also didn't help that it was the first time that one of the parents was gone for an extended period and the parent that was left home (Tom) had never had to deal with all the kids on his own. Also, the only time we see complete chaos in the house is the first day that Kate has been gone. After that the kids are more behaved (at home).