An excellent documentary by German sexuality expert, Oswalt Kolle.
The programme does not shy away from the subject and features frank and open discussion with Kolle, his wife, his teenage son and daughter, and his 4-year-old son. Most of the discussion takes place on a German naturist beach where the whole family are, naturally, in the nude.
Note: You need to be able to understand German, in order to get the most from this film. I have, as yet, not been able to find an English sub-titled version.