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.
Continuity mistake: 35 minutes into the film, Cher enters her bedroom with a bowl in her right hand and a bottle in the left. When she gets into bed, both have switched hands.
Revealing mistake: Near the end of the film when Charlotte and her mother are having the row, Charlotte receives a huge slap. Play the slap in slow motion, and you can see that the mother misses Charlotte's face.
Other mistake: Near the end of the film, Charlotte and her mother (Mrs. Flax) are having a blazing row. Mrs Flax calls Charlotte 'the town tramp', and Charlotte retaliates by telling her that the town already has one. This results in Charlotte receiving a huge slap. This slap would leave her cheek as red as a tomato, but as the scene continues, there isn't a mark on her face. A tad unrealistic?.