Factual error: Though extremely modest by today's standards, the dress worn by Clara at the hoedown shows far too much cleavage for the time. No schoolteacher would ever wear a dress like that in the 1880s.
Factual error: When Kevin's mom leaves Paris to return home, the plane shown departing the airport is a DC-9. No airline uses this plane for trans-Atlantic service - it doesn't have the required range.
Suggested correction: Although not explicitly mentioned, it could easily be a connecting flight which departs Europe from another airport. Potentially flying a short or medium range aircraft to reach a hub airport like Heathrow, then catching a trans-Atlantic flight back to the US.
Factual error: During the second half of the film, set in Britain, Peter Mitchell is hiding away from a woman. She opens the door and asks "What are you doing in my closet?" She seems to talk with an upper class British accent, but she wouldn't use the American word "closet," but use either "wardrobe" or "cupboard."
Factual error: When the police chief is looking at Danny's police file just before calling his father, you can see a few different phone numbers listed. These numbers are all using 213 as the area code which is for Los Angeles, CA. Given that the film takes place in New York City and that the addresses listed on the same police file are NYC addresses, the phone numbers should be using 212 area codes. (00:28:22)
Factual error: When John Ritter and his wife are sitting with the fertility expert, the doctor explains how her reproductive system is not functional. The manner in which he explains this would lead us to believe that she would have been physically unable to menstruate, thus she would have known long before this meeting that she was incapable of bearing a child.