Continuity mistake: Right after Clooney picks the kids up from pre-school. It was superhero day, so the kids are dressed in homemade costumes. If you watch the little girl, she changes back and forth between superhero and little girl within the blink of an eye.
Other mistake: One of the extras is seen in two different scenes. The same woman is seen first at the beauty spa and then later at the police station.
Factual error: When the cell phones are switched, Melanie's mom asks Jack what his cell is and he says Pennsylvania-something. The old-fashioned system, over a half-century old of having a two-letter denomination for the area or town, such as PA for the area around Penn Station, or LI, for Long Island, is followed by five digits, but Jack gave four digits, so it wouldn't have been an actual phone number.
Plot hole: When Clooney gets the call from Melanie's mother, he calls Melanie to let her know that her mother can not watch her son. She asks how he got her phone number, implying that she did not know that the phones were switched. Right afterwards she tells him he has a meeting at five. How did she know that he had a meeting if she just found out that they switched phones?
Continuity mistake: When Jack and Melanie are arguing and waiting for a cab to get to the soccer match, the kids interrupt them and you see a cab is waiting. The cab is a Ford Crown Victoria. They are then seen traveling in the cab, which is now a Chevrolet Caprice, which they exit before Melanie goes to her meeting for drinks.