In reply to RichG:
Interestingly, I seem to set 'reachier' routes than my tall colleague. I am about the height of your average 10 year old, and I often get told by taller adults that my routes are really tricky. I think that what is a reasonable reach for a child (or me!) becomes either too low, so therefore cramped, for a taller person, so they then try to reach through to the next hold, which is very reachy. So I wouldn't hesitate to set for the kids' reach, or get a midget to set for it. My boss tries to make sure he can reach everything with his elbow to make sure reach is short.
Adding in balancey moves works, and smaller holds (not so hard for the kids as their hands are also smaller).