Continuity mistake: When Molly takes Mikey into work and he is under the desk, Rona is still wearing her shoe. Yet when the scene changes, her shoe is missing when Mikey starts tickling her foot. Then when the boss realises that Mikey is under the desk, her shoe is back on. When the shot changes again, her shoe is off.
Other mistake: Right after Julie is born and they're taking her away, the nurse is opening the door. Then they change over to the mother, then back to the baby, and the nurse is just opening the door again.
Continuity mistake: When John takes the kids to the movies and is trying to weasel some free popcorn, it is obvious that someone shakes the baby girl to make her cry.
Other mistake: In the scene when Mollie, James, Mikey, and Julie are in the restroom together, Mollie tells James (who was shaving) to hold Julie while she explains something to Mikey. While James reaches down to grab Julie, he has shaving cream on his upper lip. But, when he comes back up, the shaving cream is gone.
Continuity mistake: When Mikey is underneath the desk and goes to put white out on the man's shoe there is already white out on the shoe. Probably from a previous take.