PG stands for Parental Guidance. This means a film is suitable for general viewing, but some scenes may be unsuitable for younger children. A PG film should not disturb a child aged around eight or older. Parents should consider whether the content might upset younger or more sensitive children.
But that doesn't mean that the film will be of interest to a child, just that there have nothing that should upset them or that you wouldn't want them to see.
The child (8, 10, something like that) behind me at Life of Pi was clearly bored.