I remember my first Mastermind set as a kid - I loved the game!
Mastermind is a two-player game. One player is the codemaster, the other is the codebreaker. The codemaster chooses a secret code, the codebreaker tries to crack it.
Before you being to play, you need to decide how many possible letters there are in your code. The original Mastermind used (if I remember right) codes made of four or five colored pegs. You could just as well use letters or numbers - but stick to codes of between 5 to 8 different letters, about 4 or 5 long.
Once the codemaster has chosen a code (it's a good idea to write it down somewhere the codebreaker can't see it!) the codebreaker starts to guess codes.
After each guess, the codemaster tells the codebreaker
For example, if your code was FBEF and I guessed BACF, you would tell me I got
In my opinion, kids have to be about 8 or 9 years old and up to properly understand the rules of the game, or think logically about what information the codemaster's responses gives them.
You just need a pencil and paper to play this game - one piece of paper for the codemaster record his or her code, another to record the guesses and responses. You can also buy boxed mastermind sets, of course! My website has a java applet that lets you play mastermind against the computer, either as the codebreaker or the codemaster.
You can see if you're smarter than the computer! Or just use my online mastermind game to practice and improve your codebreaking skills!