Worldwide Secret Code Puzzles for Kids (Dover Kids Activity Books)

U.S.A. Secret Code Puzzles for Kids (Dover Children's Activity Books)

Break the Code: Cryptography for Beginners (Dover Children's Activity Books)

Codes, Ciphers and Secret Writing (Dover Children's Activity Books)

Secret Codes for Kids: Cryptograms and Secret Words for Children

Top Secret: A Handbook of Codes, Ciphers and Secret Writing

U.S.A. Constitution Activity Book (Dover Children's Activity Books)

Spy Science: 40 Secret-Sleuthing, Code-Cracking, Spy-Catching Activities for Kids

The Everything Kids' Games & Puzzles Book: Secret Codes, Twisty Mazes, Hidden Pictures, and Lots More - For Hours of Fun!

Brainiac's Secret Agent Activity Book: Fun Activities for Spies of All Ages (Activity Books) (Activity Journal Series)