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.
Factual error: When Kevin's mom stays behind at the Paris Airport to wait for a flight home, she is shown in a gate area in front of a huge picture window. Outside can be seen an aircraft, a 727 in Eastern Airlines livery, in what is actually Chicago's O'Hare Airport. Eastern never flew to Paris and the aircraft would not have the range for such a flight. Also, you can see a sign that lists Terminal E and F, which are at ORD. They do not have these at Paris ORY.
Factual error: Assuming the McCallisters left Chicago mid-morning as the story suggests (say, between 9 and 10am), and allowing for an 8 hour flight and 7 hour time difference, the flight should be arriving in Paris somewhere between midnight and 1am. However, the footage of the plane landing suggests it is around twilight.
Factual error: In the scene where Kevin swipes the toothbrush from the drugstore, he slides across a skating rink on his knees while being chased by the cop. Ice is slippery, but not THAT slippery (especially when it's been skated on). Kevin would have only slid a few feet before coming to a stop.