For the tone of the movie, I think a fairly reasonable comparison could be made between it and The Haunted Mansion (the ride). For the most part, I'd hazard a guess that if your kids can handle the ride well, there's a good chance they should be able to handle this movie. Both are a little scary in a fun way, if that makes sense. There are some cartoonish gruesome elements in the movie, as already mentioned by pervious posters, but the movie isn't gory, and there aren't really any "jump out and scare you" elements either.
In some ways, it reminds me of Monsters Inc. Both Monstropolis and Halloween Town are populated by those who make scaring their business, but they aren't evil -- it's just their job, more or less. And each has an exception or two to that, who serve as the villain(s) for each film.
SSB