I watched this with my 9 year old son, and the first time we watched it, we were surprised at some of the frightening scenes. The next day though, we were able to laugh about them, and this has now become one of our favorite movie-night picks. Some of the scary things could be when the baby morphs unexpectedly, or a grown man voice comes out of the little baby's mouth, again, unexpectedly, things like that. Maybe watch it first to see if your children might be frightened.
But all in all, it's a pretty fun movie.