Staff at Cineworld cinema in Brighton Marina, East Sussex, dialled 999, accusing the seven girls of breaking copyright laws by making illegal recordings – acts the staff described as an 'emergency'.
But when officers examined the girls' mobile phones they couldn't find any evidence of wrongdoing and they were released.
Four of the girls were so upset by what had happened, they wouldn't go back into the cinema and were left to wait outside in the dark for their parents to pick them up.
Louise Lawrence, 52, whose daughter Tanith was among the group, told the Mail: "I feel absolutely furious about it. Three of the girls didn't even have mobile phones. They were separated and interrogated by the police.
"These are children who have never had any contact with the police before, so they were absolutely terrified. "Afterwards my daughter said to me, 'Mummy I was too frightened to even cry'."
Sussex Police have since apologised for any upset caused and sent a sergeant to the girls' school to explain why they decided to attend the incident.
Some of the parents have now written to Cineworld to complain about the treatment and the cinema's refusal to refund the children for missing the film.
Louise added: "What worries me most is that it was around 7.30pm and it was pitch black.
"Neither the police nor cinema staff had bothered to call their parents after the incident, even though they knew they were children and only 12 years old."
A spokesman for Cineworld told the Mail that the cinema chain had contacted the parents and 'apologised for the distress caused'.
She added: "While we regret that the customers felt distressed, we are confident that the correct procedures were followed.
"If our staff see such behaviour we expect them to notify the cinema management immediately and to call the police.
"However, we have taken on board the concerns expressed by the parents and we are reviewing how the policy is applied to younger customers."