Children and Chess

Two of my children (16 & 11), have shown an intermittent interest in chess. At these points in time I have taken the opportunity to actively encourage them to play. By playing games with me or using chess software on the computer. They both know the basics and are able to play a reasonble game given their ages. 

Eventually their current interest will fade and they will move on to the latest thing. I feel my approach should be to just wait until they come back chess - I don't want to put them off forever by being too 'pushy' about the game. Any ideas/suggestions anyone on the best way of encouraging children to increase their interest and improve their game.

I would really love for one of them to one day beat me fair and square!