This is a movie with lots of gross monsters, spirits, witches and magic.
It gives you a great insight into Japanese culture and mythology.
And it is a really great story. In fact this is the best animated movie of all time.
I am sure that many kids younger than 5 will enjoy this movie (kids generally like gross monsters and the mild level of violence in the movie), but may be disturbed or confused by it afterwards.
This is definitely movie to watch with your kids, and talk to them afterwards. This is not a Disney movie. It has a complex plot and complex themes. My judgement is it is best to wait until your kids are old enough to understand and talk about the issues in the movie with you.
This is not a movie where the good guys kill the bad guys.
Rather it is a story about a spoiled girl who is forced to overcome her fears and her selfishness to rescue her parents. Both she, and the other people around her (both the nice and not so nice ones) are transformed for the better though the story. It is not a movie that shows any ambiguity about good and bad, but it does show that even bad or flawed people are redeemable.
Of all the movies in the commonsense media database, this has one of the widest range of reviews. In part because for many of the reviewers this possibly the first Japanese anime they have watched, and the Japanese do not play by the same rules was Disney or Warner Bros, neither in their plot line, their mythology, or in what is normal to have in a kids movie. Secondly many parents are very sensitive to anything gross and want to protect their kids from it. So they find the scene with the river spirit vomiting up all the pollution that has made it sick very gross. Great children's writers like Hans Christian Anderson and Roald Dahl have recognized that kids & toddlers love this kind of gross. To further the irony, one of the themes of the movie concerns an overprotective parent, placing her baby in a protective prison away from germs and other harmful influences.