Factual error: At the start in 1989, when Mike is dancing with the cheerleaders and also just before he goes after Scarlet, in close-ups of the crowd cheering there is a man (with a white baseball cap) wearing a Paramore t-shirt. However, Paramore (a Grammy-nominated American pop rock band) formed in 2004. The style of t-shirt he is wearing is actually one of the officially licensed Paramore merchandise. (00:02:45)
Factual error: When Howard is running after the bouncy ball he is on the second floor of the Mall of America, however, you see him run through the LEGO store which is located on the lowest floor of the Mall of America, which is impossible if he was on the second floor before.
Factual error: Near the beginning of the film there is a map of Europe with the countries coloured in using their respective flags. Great Britain is coloured with the Union Jack (Union Flag) pattern but so is the Republic of Ireland (Eire). The Republic of Ireland is not part of the United Kingdom (the political state) or Great Britain (the geographical term for the island), only the British Isles - they are a separate country and the Union jack is not their country's flag. Only the north or the Irish landmass (Northern Ireland) and Britain should show the Union Jack. If they are using an "old map" it would have to be very old, before the 1920's.
Factual error: If we are to assume the film is in chronological order over the course of a single school year, then why does the football scene come after Christmas has occurred? High school football season ends well before the holiday season. (00:47:00)
Factual error: Milo gets out of the car to pump gas, but they are in New Jersey where pumping your own gas is illegal.
Factual error: There is a scene with several flags hanging on the wall of the castle. These are supposed to be flags in the Middle Ages. However, one of them is the present day banner of the Hungarian Republic (where part of the movie was shot).
Factual error: Dinky Winks has a branding iron that says 'Dinky' when it faces out, but we should be reading it backwards. When he uses this brand, then it will be backwards.
Factual error: When Dave is at the Yankee game and he is telling Linda he wants to marry her from the field, it is impossible for his voice to ring throughout the whole stadium without a microphone (even though it echoes as if he were using one.). Similarly, he wouldn't have been able to hear Linda when she shouts "I'm over here." (01:26:30 - 01:27:45)
Factual error: In the opening shot of the film, a big oak door opens - carved in it is the date 1862 - 42 years after George III died.
Factual error: One of the main characters has a Harley Davidson. The movie is supposed to take place in the fifties. The Harley had an electric start primary cover which wasn't made by Harley until 1965.
Factual error: Cher complains that Astroturf is going to ruin baseball. Mermaids is set in 1963 when Astroturf was still being developed under the name Chemigrass. It wasn't christened Astroturf until it made its world debut on the floor of the Houston Astrodome in 1966.
Factual error: A video is shown of Derek Huff singing "Ice Ice Baby" at a school talent show that took place when his brother Brennan was 17. Robert states his desire to retire in "in two years," in 2010, making the movie's setting 2008. Brennan is 39 in the film, placing the talent show 22 years ago in 1986. The song "Ice Ice Baby", recorded by Vanilla Ice, came out in the summer of 1990.
Factual error: At the end of the film, when Ramu is on the Sally Jesse Raphael show, even if it was being broadcast live in New York, it certainly wouldn't be broadcast live in India for his family to watch. Also, India is 9 1/2 hours ahead of New York. If Ramu's family are watching the show when it's daytime in New York, it's awfully light outside!