This is my scratch pad for ideas for games, starting at the very simple and getting more complex.

 

You don't want to prescribe the games the kids write, just give them ideas and get them to build their own.  They will likely be more motivated to make a "Doctor Who" or "Hannah Montana" version of something than just replicate an existing game.

 

Try and encourage them to do the artwork in their own time rather than lesson time as it doesn't need supervision, perhaps get them to bring in images on a USB stick; there are some good collections of icons to be found on Google images, often with relaxed licencing.

 

A classic and quite easy to program game.

Pong

(http://en.wikipedia.org/wiki/Pong), only three sprites (one for each paddle and one for the ball), two variables (one for each player's score).

Kids might need a hint on how to do the maths to properly do bouncing off the paddles.

 

Have a boat that can more left-right on the surface of a sea, a submarines appears and moves right/left across the scene below the sea, player moves ship  and drops a depth charge which sinks and may blow up sub, three sprites: one for the ship, one for the depth charge, one for the sub (which gets re-used for different subs each time, change the colour and the size/costume to make it more interesting).

Extra marks if subs can shoot torpedoes at the ship.

 

 

http://en.wikipedia.org/wiki/Breakout_(arcade_game) use stamping to create the blocks from a single sprite.