National Treasure: Book of Secrets (PG) is both campy and campground. Its American history is hokum. The plot depends on an easy break-in to the Oval Office, an easy kidnapping of the president from a dinner party, a City of Gold under Mount Rushmore, a book stashed in the Library of Congress that contains the truth about the Kennedy assassination and Area 51 of UFO fame, etc., etc. - but no one takes any of this seriously.
What's makes this film fun for the whole family is the campground part: It's a throwback to action movies without sex, violence, bad language or hatred of America. Nicolas Cage as Benjamin Franklin Gates gives patriotic talks and risks death to prove that an ancestor was not a John Wilkes Booth co-conspirator. Binding up the nations' wounds also leads to a binding up of familial wounds: Is it a spoiler to report that Gates's estranged parents reunite, he and his estranged girlfriend reunite, etc., etc.? I don't think so, because all of that is eminently predictable, and it's still fun to see fine actors such as Helen Mirren and Jon Voight having a good time as they and the producers laugh their way to the bank.