Factual error: No airport in NYC has the view of the New York City skyline that Kevin has when he realizes that his family is in Florida and he's in New York.
Factual error: When Kevin goes in the limo, the front desk manager attempts to process a charge on the credit card, which comes back as "stolen." No credit card terminal flashes "stolen" when a credit card has been compromised or cancelled. The machine would simply decline the transaction, much like if the credit limit had been exceeded, or tell the merchant to phone for authorization.
Factual error: The picture that Kevin takes of Marv and Harry through the toystore window is perfectly clear. There is no way you can take a picture of something through a window without the flash reflecting back and ruining the image, especially from as close a range as Kevin was.
Factual error: When Harry and Marv arrive for the first time at Kevin's "funhouse", they look up to the roof and spot Kevin taking a Polaroid of them. The flash brightly illuminates them both, but the building looks to be at least 30 feet high; a basic Polaroid camera does not have a flash strong enough to reach such a distance (plus the street is already illuminated by lamps and Christmas lights). (01:23:05)
Factual error: The AA flight number to Miami is a 4 digit number beginning with a 5. These are regional flight numbers but the family flew on a mainline 767.