I went to Berchtesgaden a few years ago, which was really nice. Lots of outdoor activities, you could go up to the Eagle's Nest, if the buses are running, the salt mine is quite nice, too.
Lake Königssee is beautiful, so you could take a boat trip on there.
And Salzburg is only 40 minutes or so by bus away.
I stayed at the Explorer Hotel, which was reasonably priced and is a fairly new, eco-friendly hotel.
Two years ago I went to Garmisch-Partenkirchen. You've got mountains, Zugspitze, Alpspitz and the Wank (yes, really, they are aware of the connotation) , Partnach Gorge, the old Olympic Stadium and the Ski Jump.
Nearby you've got Linderhof Palace, Ettal Monastery, Oberammergau, Eibsee and Mittenwald. Not too far away is Innsbruck in Austria, I think it took me about 40 minutes by car.
Both Berchtsgaden and GaPa could be done in combination with Munich, but for both I'd recommend a car, it makes getting around a bit easier.
For the Black Forest, it really depends on where you are going. In the South you've got the Lakes, Titisee and Schluchsee, the Feldberg, the highest Mountain in the Black Forest. In Titisee (town) there is "Badeparadies Schwarzwald", which is a large Waterpark
Just be aware that some locals in the South of the Black Forest speak a dialect which is closely related to Swiss German, so they can sometimes be a bit hard to understand but will usually repeat themselves or try to speak "high German".
Between Freiburg and Offenburg, there's Europapark, Germany's biggest themepark, which might appeal to your DS. Europapark
Further towards the North of the Black Forest there's Baden-Baden, Freudenstadt, Calw and Bad Wildbad, which are lovely.
Lots of hiking trails all over the Black Forest, in varying lengths and difficulties.