The kids will like the BMW museum and it is right next to the Olympic Park. You can easily spend a couple hours there. It is easily accessed by the subway. You'll walk around Marinplatz and the day will be gone. Most retail stores are closed on Sunday so it is a good strolling day. You should definitly stay either near the hofbahnhof(train station) or Marinplatz for easy access to the airport. The S! or S8 are the trains to take from the airport to these areas. It is a easy city to get around.