I suspect we'll have a Batman Returns
effect in that some parents will take their kids to see it because "it's Batman" and then complain that the film was too dark and (how dare those movie people!!!) not appropriate for little kids. They will also claim that the film was not advertised as such.
Although, in fairness, if this movie is not for kids, how come every toy store is filled with Dark Knight
toys? Kinda sending mixed messages there.