We did this bike ride last year, that is me and my partner, we enjoyed it and wondered if you knew about it. It is a bike ride ride starting from different places all over Berlin (and surroundings) all going to Brandenburg Gate. Check out http://www.adfc-berlin.de/uploads/EY/-f/EY...nfahrt-2008.pdf
It is family-friendly, free, and your only chance to cycle on a German motorway! Last year it was a quarter of a million people creating a massive bike traffic jam. try it out!