Well, lots of experts on this forum..but I would humbly suggest getting this DVD and following the suggested exercises as foundations for instruction to 7 and 9 year olds..
it is the most popular clip on skiing on YouTube, if you have never seen it, here it is:
and if you do appreciate how simple the guy makes it(subjective naturally with due respect to you and anyone else), 7 to 8 year olds will get it, the point of the exaggerated moves are to get the ignorant, the neophyte, the child to gain the sensations of skiing and the feel for the edge, anyway, its a worthy 20buck investment..to help create lessons.
And if you want to see a 7 year old practising these moves on his 1st two days of skiing this season to get his legs back (this 7 year old is a pretty advanced big mountain skier) ... he still goes through the KM moves to get the feel back after the hiatus since last season (video is long, so scroll through, the fun begins kind of at 2min 30 sec point and so on), the skies are lets say a bit long for him too...20cm longer than his last season's skis.
Just a Dad who is learning every day himself, and has seen many great instructors , but in terms of getting through, to kids to
(a) keeping their hands forward (uphill hand over uphill ski) which creates counter,
(c) riding on the edges
(d) smear to steer
I could go on, I am no instructor but as a student and father, that would be my feedback, the KISS principle, get the kids to gain the sensation fastest without super-technical discussions and exercises.