Good morning.
Now that is one of those questions which stretch my imagination to the limit.
I believe you have two small children.
Are you looking for Gymnastics for yourself?
Or are you looking for a Sport Club for yourself?
Or are you looking for Mother and Child gym or Children's Gymnastics for the daughters? (Click on Jugend > Kitu oder Muki)
Ostermundigen for yourself and the girls under the same headings as above.
Hope some of this might be useful.

P.S. if you add a couple of tags - gymnastics child/adult this post might help someone else asking the same questions.