Thanks Bob and lostinidlewonder

I think I might just stick to the listen and learn by ear technique I've been using for the past few months of lessons... The thing is I teach in a music school and the parents want 1 on 1 lessons, I would love to teach keyboard classes for beginners, first to save time, second so that they have healthy competition, third so they are all interested to learn as a class, with "homework" and scheduled activities and group work...
I'm just a little worried about this aural learning, I have a student who learnt by ear from very early on with Suzuki, and she came to me with very poor music-reading skills, she could often pick out that she made a mistake from learning with the recording and imitation, but had no idea if she was going by the score. We're now doing a whole course with studies and fun and easy pieces with method books to improve score/music reading and materials I've written myself. But it is such a hassle and takes AGES for her to learn something new.
I don't want my young beginners to end up like this. When should I encourage my very young beginners to read music? When they can read better? They understand the keyboard's "high" and "low" concept and I often give them short little pieces that are songs, so we do some singing and clapping first to know what it sounds like, and then they get on the keyboard and imitate the sounds. They seem to love this and I do heaps of these activities with them. However, the parents really want their children to play something with both hands, and to read music so they can enjoy what they were playing, and hopefully attend those little performances we set up at the school for students.... Maybe I'm just a little impatient because I feel I'm letting the parents down by not helping their kids to improve faster by playing proper pieces...
That is also the reason why I get a little angry at the parents and not the kids for not doing any work at home, its as if they want me to do the work in lessons and make them learn something fast when they don't put in the effort at home. The kids love the lessons though, they learn heaps of stuff and have a very healthy attitude towards becoming little maestros

But I feel like I"m repeating myself every single lesson, or for at least half of the materials we worked through the week before like lostinidlewonder mentioned.
I can't use bribes because they don't really care, they get pretty much everything when they go home, and I think they're too little to care about that sort of stuff.. I've tried this before and only found it slightly effective (with Harry Potter stickers, badges, and other merchandise :p)
so in summary, after all that ranting, my problems are
1) when do I encourage learning and reading of music?
2) I have too much pressure from parents and the school to teach the young beginners something they can play for mini concerts or at home for guests, yet the progress is slow because I am repeating myself every lesson, while they don't do much work at home at all. I don't want my lessons to turn into "practice now" lessons, but rather, "learn something new" lessons
3) The kids get pretty much everything when they go home, very well-off families, (private music school), and I cannot encourage them with bribes or "stuff", I'm not allowed to give them lollies or chocolate as school policy. The kids love the lessons, they just don't feel the need to do anything after the lessons have finished, (nor do the parents

)
I feel like giving up, it is VERY tiring, and I feel like the school and parents are not giving me support or realistic expectations.....
I learnt the piano when I was 4 too, I remember learning by ear and imitation, but then I would try to see and learn how I got those notes from the score, and eventually I progressed very fast because I could and wanted to read music, and loved learning new and more difficult pieces. I am afraid of my students getting "stucK" anywhere in the future from insufficient knowledge of music from earlier on.

I want them to see the fun in learning music, as a second language almost, so they feel the want and need to learn. I don't think they are incapable, I do think they need a bit of a push, their reading isn't that good but at least they can use their memory and recall for notes and note values, right??