Mt Rushmore area w/kids 3,6 and 17
 

As you can see, we have a wide age range of children (3,6,17). We plan to camp at Flinstones Bedrock City campground in Custer for two nights. What would you recommend as activities/must-see things for our family? Never been here and want to get a good feel for the area while taking into consideration young children. Traveling on to Colorado after this excursion. Suggestions would be helpful! Thank you :)

Go see Crazy Horse. http://www.crazyhorsememorial.org/monument/

I'd recommend spending a lot of time at Custer State Park. The drive around the Wildlife Loop would be good so you can see bison and prairie dogs. There are a number of good trails for hiking (although you might have to carry the 3y.o. part of the way). We've done guided horseback trail rides from Blue Bell Lodge, but unfortunately, your youngest is too young for that. You could rent paddleboats and/or rowboats at Sylvan Lake, which is lovely. There's also a hayride/cookout from Blue Bell Lodge that the whole family could enjoy.
See the following websites for details on these and more activities at Custer State Park and Custer Resorts:
http://gfp.sd.gov/state-parks/directory/custer/
http://www.custerresorts.com/index.php

let the 17 year old do a wild cave tour at wind cave or jewel cave

My parents took me to Custer State Park each summer for 4 years. Those are some of my best memories. DO not skip this park. Take some cereal with you, if you run into a pack of burros the kids will love to feed them, but keep in mind they have no sense of personal space and will stick their heads in your vehicle. Keep your distance from the bison, they are not tame. The praire dog town is cool and they will get close to you if you have food and are still. The badlands are close by. If I remember right, Jewel cave is better than rushmore cave. We are taking our 3 boys (9,7,3) in a few weeks and here are some things we have planned:

http://www.bearcountryusa.com/ http://jewelcave.areaparks.com/
http://www.mammothsite.com/
http://www.reptilegardens.com/inform...s-location.php
we will also visit Mt. Rushmore, Crazy Horse, and the Badlands. We are actually staying in Custer state Park for four nights. Besides bison, burros, and praire dogs, they also have bighorn sheep as a common site. Check out needle highway in the park.