The Martell distilleries tour is very interesting and lasts an hour, focussing strongly on Martell’s history, the distillation and grading process, finishing with a complementary drink for adults and face-painting for kids. Tours are in Enlish or Fench. Pre book or just turn up- but be prepared to wait for an English tour. The town of Jarnac itself (where the distillery is) also has some wonderful cafes and restaurants for lunch and a small adventure park for children. You can also take river tours here which makes the drive-time more worthwhile.
Website: http://www.martell.com/cognac-guided-tours.asp