CIA's own SpyKids program - take a look at the recommended reading material apparently your kids should know to be CIA safe

http://www.cia.gov/cia/ciakids/history/k-5books.shtml

5th grade reading list

How to Write and Decode Secret Messages
DK Readers: Spies! (Level 3: Reading alone)
Wanted Dead or Alive: The True Story of Harriet Tubman