Well, it down to this or Expendables 2 today, so I saw this instead. It's a damn good little movie overall. I've also seen a reviewer say it should have been PG-10 (kind of inbetween PG and PG-13), not PG, and I think he was right.
There are a few scenes that actually made me uncomfortable (in the good way, because I like being scared/unsettled), and I was just thinking that young kids might have crapped their pants. Even the opening scene, a movie within a movie about a girl getting her brains eaten by a zombie, might be a little unnerving for kids; it depends on the kid.
The "humor" in the movie starts out more on the subtle side, like a "sad sweet funny" movie at first (situational/juxtapositional humor), until the jokes become a little more direct and LOL'able.
Norman's more like "what if the sixth sense kid actually was okay with gore and wasn't scared of the ghosts" at first, but it still isolates him in just the same way and he's a pretty lonely and misunderstood boy.
One thing of interest (and kudos) is that the animators didn't choose a conventional style or a style that was polished; some of the characters are actually a bit grotesque, and not in an overdone way. Even with body shapes, no one's got this convention "perfect" body shape, and even the two characters with a potentially good shape (the two older teens) are still both kind of distorted. Even Norman's nose isn't straight on his face; it's crooked at the bottom, and a little off-center. I bring this up because I think this aspect of the style reflects on the whole movie in general: It might look familiar at first glance, but it's really all kind of grunged-up, un-idealized, and more about average normal human beings as you'd run across them every day, flaws and perks and blemishes and positives and all.
Another of interest is that they really didn't use a lot of well-known/established stars for the voice work. The lead was the kid in the American adaptation of "Let the Right One In," and Anna Kendrick (a decent supporting actor in the many many movies she's been in) plays his sister, and John Goodman has a partly unrecognizable cameo; Casey Affleck and Chris Mintz-Plasse are in it too, but again they're not your $15 million / movie stars that we typically get seen billed in movies like this. I hope a trend continues of not just shoving your top box-office names into an animated picture, but actually casting people who fit the parts well.
I think the only false note in the movie is the little speech before the courthouse about bullying that Norman gives later in the movie; it was a little long and too direct. The movie does best when the points are being made through inference; fortunately, there are a number of those moments as well. Norman's first and final encounter with the "witch" is actually one of those moments, where you're fairly certain what is going to happen, but the interaction is just really real and gives a true sense of how high the stakes actually are and how they could go wrong, and how brave Norman is actually being.
I think the audience is more older kids (10+) and their parents; younger kids will laugh at some of the jokes in the movie, but I honestly think they could have nightmares coming out of it, depending on their age and maturity level.
Ending credits have a neat art style (and margin art).. and there's a small but rather cool bonus if you stay through to the very end.