Someone just emailed me with this question. My first reaction was 'if you don't have a clue, then you shouldn't be trying to do it', but then not everyone has my unbearable self-confidence that they can do things before they try, and it may be that someone running a chess club doesn't actually play much chess themselves. So...
In an ideal world, your young chess players will pair up and play in various combinations all evening, without much need for interference, either in friendly games or in your internal competitions, or you might organise an impromptu Swiss Blitz. And if you have a member who doesn't fancy playing today, you can set them to work through a page of tactics puzzles, or endgame exercises, or to play through the bare score of a master game and make notes...
However, things can go wrong with this picture. Some youngsters just aren't good enough at chess to enjoy any of your fancy exercises. And in the case of my own club, I often have relatively few players turn up, but all with wildly disparate strengths, and all having played each other too often to be very interested in doing it ever again. This is when you need...
Time handicap. If a 12-year-old faces a 7-year old, the younger player gets 12 minutes on the clock and the older gets 7. Or, if they're not ready for clocks, then the older player gets 7 pieces to play with and the younger gets 12 (the standard 8 plus 4 extra minor pieces).
Material handicap. Or, just let them play one quick game. Count up the material at the end of the game, and if the winner finishes with a queen and rook extra, remove the queen and rook for the next game. If the stronger player wins again, take away more material, until the weaker player starts to win.
The weaker player gets a chance to turn the board around at any time (except mate in one). Or two chances. Or three chances...
Get the strongest player to play a simul.
Make the stronger player play blindfold (only the strongest players will be able to do this).
You will probably find that the best chess players excel at variants, but when everyone is beginning, it's a useful leveller. Also, the key to success in each variant may be something that is useful to be reminded about for when you return to chess proper.
First check chess. First check wins! For players reluctant to sacrifice...
Losing chess (suicide chess). Players need to spot attacks and plan sequences, both good chess skills.
Kriegspiel. The best way to play involves careful preparation of an attack with a large combined force whose members mutually defend themselves. (Then get them to play a chess game where they try and do that.)
Japanese chess (Shogi). Slow, but you do have to use all your pieces to attack.
Chinese chess (Xiangchi). For those players who think rooks are mere paperweights (placed in the corners to stop the board rolling up, and where they must remain for the whole game)... Chinese chess is fast, tactical and depends on getting your rooks (chariots) and cannons into play along open lines.
Daft chess. Crazy lightning. Card chess, where which side gets to move at each 'turn' is determined by a turn of a card: red=White, black=Black. Active chess.
There are some here. I understand in Iceland they have a little series of graded endgame exercises that you can work your way through for a certificate. There are other certificate schemes. I've just composed a little set of exercises to develop the most basic chess skills of spotting attacks and undefended pieces, but they're graded so that better players can attempt the more complex puzzles.
One week, faced with the same three faces as last week, I got them to ...
Brainstorm all the things you need to know and do to be a good chess player.
Select the one of those things that you do least well and is the reason you lose most of your games.
Give yourself some advice, write it down on a piece of paper, and prop it up by the board when you next play a game of chess.
I actually then played a simul against the three, where the result was determined by how well they followed their own advice: failure to abide by the advice they gave themselves resulted in instant loss of the game, but success meant I lost.
Quizzes. Take a while to work up but can occupy a whole evening. Good for the end of term.
Puzzles. There are loads of books of these, but the best thing I ever did was buy a tear-off chess calendar from Robert Byrne with a fairly straightforward puzzle a day from actual play -- some mates in one, mostly mates in two, and so on. The joy of this is that I can hand out the diagrams and collect them in when they're completed, no need for multiple copies of books, no need for photocopying... magic.
How good is your chess? Just in case you haven't come across this: you take a game that might be fairly brief but illustrates one or more themes that you might have been discussing recently. Then the players take a board and take (say) the white pieces in the game and after (say) 10 moves, ask them to guess white's next move, and write it on a score sheet. OK, the actual move was X, which was a good move for three reasons, and you get three points for choosing it. However, if you chose Y, that's worth 2 points, Z is worth 1 point, nothing for anything else, and if you allowed Black to win material, you deduct points according to how much material you lose (pawn=1, bishop=3, etc.). Master games are useless for this, you need ones easy to understand, so old junior games are best, but you need to be an OK player to be able to assign points fairly to different candidate moves. You also need to recognise when a move suggested is actually better than the move chosen in the actual game.