I have a few suggestions that might make your kids motivated to learn and to practice. Some of these I thought up on my own, and one of them I did not. I got the idea from someone on the piano teachers group on yahoo.com

Piano Karate:

Just in karate you go through different tests and trials to earn different belt colors, you can use bracelets for piano karate.

EAch time your student comes to the lessons prepared, memorizes music, or practices every day, they are awarded points. Certain points achieve certain bracelet colors. I have 10 different bracelet colors. The kids have really enjoyed this and have turned 360 degress from not practicing to waiting at the door with books in hand. You can also adjust this to your own lessons and award them points for achieving certain things (like remembering all the notes of the white keys). The kids love the challenge and make them self motivated.

MAT GAME:
For teaching the staff, I've created a mat with a drawn staff and big fat notes they can stick on. One side of the mat is for the treble cleff and the opposite side is for the bass cleff. Kids love this, and you can do lots of things with it. My students like to make up songs with the notes and then play them on the piano. We also practice intervals (1-5) and play them. You can make half notes with white construction paper and a black line around the note and quarter notes in black.
You can also makes notes with the letter names on them to help them remember where they put them. You can make a mat with the note names on the lines and spaces so they can match the note to the line.

When the kids get really good at remembering notes on the staff, you can play a matching game with them. Create bass cleff and treble cleff note cards with the different notes (c-g) in the C Major position (or whatever position you are learning) and then have them flip up a note and have to match it to it's note name. If they get stuck they can always go and find it on the piano.

Hope you can find these useful!