Despite the poor ratings and getting generally panned by the critics, this isn’t actually a bad movie. I am sure that the younger children will like this, though there are some frightening bits. The story is a retelling of Jack and the Beanstalk: a very simple formulaic fairytale, i.e. Boy, Beans, Giant , Princess, Rescue. Not too shoddy and the giants are pretty intimidating too; even for a big kid like me.
Note: there was another fantasy film with (nearly) the same title called Jack the Giant Killer (1962). It bears no resemblance at all to the fairytale or this new movie. It is worth a watch though, if only due to the fact that it scared the pants off me when I saw it as a child. It also left me with a fatal attraction to scary women.