We went to BD our last trip with a party of 9, ranging in age from 4 years to 65 years. I think that the restaurant is "kid friendly" in the sense that you won't feel out of place bringing a child, but I don't think that the restaurant has "kid appeal." The adults, I think, appreciate the decor far more than the children do. I thought the food was wonderful, but I was in the minority in my group only because the menu is somewhat limited. My mother and father, who do not enjoy "different" sorts of food ordered the steak, which was great, but they felt like they had no other choice because the menu is filled with items they woudn't ordinarily try.
In the end, if you have people in your party who are meat and potatoes sort of people, I don't know that they will enjoy Brown Derby since their options are limited. If you have the sort of family that loves to try new things, the food was well prepared and well seasoned and I thoroughly enjoyed it.