This is for pedagogical purposes. Please do not cypher actually important messages with this.

Anyway I think it can bring with little ones, and adults alike, interesting conversations around :

• secrecy
• privacy
• cryptography as counter-power
• mathematics, starting with modulo
• the duration a message can stay undecipherable and thus the kind of message to share
• computational complexity, how many permutations are available

... and a lot more!