The Black Hills is a beautiful forest full of fun trails, rivers, lakes, mountains, wildlife and more.
I suggest starting your discovery of the Black Hills in Custer National Park as the guides are better able to help point you in the right direction for appropriate discovery based on your kid's ages. Once you have mastered Custer Park (which could take days!!), feel free to explore all of the beauty the Black Hills offer in Southwestern South Dakota.
I had the best time in the Black Hills with my family. we went camping in one of the many camp grounds that they have. Everyday we did something diffent. We went hiking up Harneys Peak. This was not for young kids unless you would be planing on caryying them in ones of those child carriers on your back. We went on tours of underground caves. We went swimming in the many lakes. If you can't take cold water do not even attempt this. But everynight when we were so hot, this cooled us off so good for the whole night. We even went digging for agates and amethyst rocks. When the kids find the "Buirried treasure" it is priceless. So that is a must for kids. You will get dirty so wear old clothes for that one. This was my favorite family vacation memories.
There are so many places to discover in the Black Hills, national parks, monuments, hotsprings, camping, wildlife, hiking, and even shopping. It is a beautiful area, covering much of the western portion of South Dakota and part of Wyoming. One of the best parts for our family was listening to the Ranger tell us about the Elk and then hearing the elk bugling to one another. One could imaging crossing the land in a covered wagon and hearing the strange and mournful sounds.