No admittance allowed

During the holidays I took my children to see the second movie in the 'Maze Runner' series, only to be told that because it was a PG13 my children would not be allowed in. I argued that PG13, means that parental guidance is advised for children younger than 13, and as I, their Mother was with them surely this would be acceptable. Management would not listen to me and we were refused entry. I think clarification is needed to be given to all staff regarding the PG ratings and meanings