My tip: time with absolute full moon on the Brocken! You do not need a flashlight, you enjoy the absolute loneliness (except for the track caterpillar) and has a breathtaking view from Brockenplateau.
A nice and interesting way for families with children from about 5 years. The story of the white deer fascinates from Schierke from large and small nature lovers. There are also accompanying books for the whole "story" of deer.