I try to figure out WHY all of my students want to learn to play the piano. For young kids this is really difficult because they usually don't know why or, if they do, they can't articulate it very well. At this age however, they'll probably know and be happy to tell you. I would ask the student if there is a piece he wants to be able to play and let him play it! There are many very popular, simple classical pieces (Canon in D, Fur Elise, etc.) that everyone seems to love. They have usually heard them all of their life and if given the option to play them, they are ecstatic. To a beginner, playing a well-known, recognizable, piece is very satisfying. I would also recommend playing working on some really simple stuff too (possibly a method book), so they can be finishing pieces. If they just work on one piece for a long time they may not feel like they're getting anywhere. You also want to make sure you're teaching them all the basic theory and techniques that may be skipped if you only teach what is necessary to play the piece (different time signatures, key signature,you know what I'm talking about)