Mastermind- Classic Crack the Code Game
http://www.archimedes-lab.org/mastermind.html

Crack Hacker's Safe- Cyberchase
http://pbskids.org/cyberchase/math-games/crack-hackers-safe/

Cryptology for Kids
http://www.cerias.purdue.edu/education/k-12/teaching_resources/lessons_presentations/cryptology.html

Open the Safe- Crack the Code with Number Patterns
http://www.kidsmathgamesonline.com/numbers/codegame.html

Bulls & Cows- Maths Is Fun
http://www.mathsisfun.com/games/bulls-and-cows.html

Primary Games- Crack the Code
http://www.primarygames.com/langarts/codebreaking/

America's Cryptokids
https://www.nsa.gov/kids/home.shtml

Rebus Puzzles
http://kids.niehs.nih.gov/games/riddles/rebus_puzzle.htm

Rebuzz Plus
http://www.learn4good.com/games/words/rebuspuzzles.htm

Police Codes
http://www.happychild.org.uk/ifs/00001pla.htm

Semaphore Flags
http://www.anbg.gov.au/flags/semaphore.html

International Code/Signaling Flags
http://www.boatsafe.com/nauticalknowhow/flags.htm

American Sign Language for Kids
http://kidcourses.com/abc-signs-program/