How should I advertise a babysitting service in this area?

I know the cost of childcare is enourmous in Germany, and I am a housefrau without a job or children.

If you want to do it professional, I think you have to become a "Tagesmutter" and there are some rules to follow and a test to take.

I would start with your neighbors, maybe they know someone, etc.

You could also go to a kindergarten and ask around there. Babysitting usually goes by recommendation because nobody wants to give their kids to strangers.

Besides the German side you could advertise in the Stars and Stripes, or the Military Community newspaper.
http://stripes.com/webpages.asp?id=92

Also: if you're a Military spouse you can apply on post to become a daycare-provider. I believe you would have to go through ACS.

As for the German side if you want to ad without any cost put a note in a grocery store on the "blackboard" such as Kaufland, E-Center, TeGut. You can also go to the local townhall for them to announce it on the community blackboard. Good luck!