Thanks all for the replies and ideas. Should have been more clear: this is one stop on a long trip (+3 months, with me mainly in Asia, my wife mainly in Europe), and my first weekend with my little girl after me having been away for two months, so I wanted to spend some time with her doing things she likes.

Playgrounds, zoos above are all good -- will search the Germany forum but if there are more ideas, keep them coming please!