I have had a hard time to look for a good dance studio in Zurich as well... most of them offer only 1 hour for one class.. which cant do much in 1 hour.. warming up has taken away half of the time already.. and the programms are not as great (e.g. no limited number of students in one class caused people kicking the person next)
Zurich is a small place with very few population. They dont offer much may because there is not enough demands.
Anyway, while I was searching for myself I had popped into this site
Ballet School Zurich
http://www.tanzakademie.ch/index_e.cfm
they mentioned "children" on some page, but not sure what age exactly.....
A small town in Germany seems to have more offerring than the so-called big city zurich, Konstance(ca. 1hr from zurich) they have different levels of ballet for children..
http://www.czerner-dance.com/
http://www.tanzschulestepbystep.de/kids--teens/index.html
but ofcause its not so convenience to take the kids there all the time, same in the swiss-french part, they seem to have more and better stuff than in the swiss-german part(or zurich)
I love dancing too

dont let your daughters down

hope you'll find a good one soon.