Orthogonal to this is my all-time favourite, the paper enigma machine: http://mckoss.com/Crypto/Enigma.htm http://mckoss.com/Crypto/Enigma.htm More for teenage

Orthogonal to this is my all-time favourite, the paper enigma machine: http://mckoss.com/Crypto/Enigma.htm http://mckoss.com/Crypto/Enigma.htm More for teenagers than younger children, working with it highlights a lot of elements of cryptography. And its a real cipher, used by real Nazis! Also a great way to introduce Alan Turing.