Right off the bat, "Ghostbusters" would be PG-13 these days for language alone. The word "s***" is spoken three times, and some other choice profanities include usage of the words "b***h" and "d***." There are also sexual situations that aren't appropriate for younger viewers. Most notably, there's a scene where Ray (Dan Aykroyd) is in bed, and it's implied he receives sexual gratification from a ghost. Dana (Sigourney Weaver) also makes some sexual advances while inhabited by Zuul, saying things like "I want you inside me."
It also deserves to be said that while "Ghostbusters" is considered a comedy, it's still about ghosts and can be downright scary at times, with numerous scary-looking creatures populating the film. There's also a fair amount of smoking, mostly from Ray and Peter (Bill Murray), and there's sexual harassment, particularly when it comes to Dana and how many of the men's actions toward her wouldn't fly in this day and age.
Ultimately, parents know their kids better than anyone else, so it's up to you to make the judgment call on what you're comfortable with your children seeing. Common Sense Media suggests that only kids 11 and up would be mature enough to watch the movie, but there are plenty of comments on the site of people saying that it's appropriate for kids who are 8 and 9. Just know going into it that just because it's PG doesn't mean it's on the same level as something like "Frozen."
