I am looking for a gymnastics class for my 6 year old daughter in the Zurich area.

I have also heard about a Circus class for children...does anyone have any information or recommendations?

yeah I'd love to learn tumbling...
i am however looking for an adults class

For gymnastics class, try your local turnverein. They run tots, kids and adult classes at very reasonable prices. http://www.tvadliswil.ch/ This is the website for Adliswil - maybe they can telll you where your local one is.
For circus classes for children, Kinderzirkus Marotte (also in Adliswil) comes highly recommended http://www.marotte.ch/
Have fun

over the summer and in other vacations the Kitihof in Hausen a. A. offers circus courses with horses, dogs, dance, acrobatics, clowns etc. They just put the tent up last weekend so I m sure there s a course this summer. Check out www.kitihof.ch or I think the summer course is also available under www.sommerferienplausch.ch