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