You do have some long days of driving, but if the little one is used to car travel it should be ok.

Perhaps as a backup day 3 add Wind Cave?

Are you planning on the evening ceremony at Rushmore?

Thanks for your response.

Yes, I realize the driving is rather long,especially from the Badlands to Spearfish, but I had difficulty obtaining reservations at places that I wanted to stay at, such as Back Roads Inn and Circle View Ranch. I really wanted to avoid chain hotels if possible. I am open to suggestions, especially concerning accomadations.
The child is a stellar traveler.
I was planning on an evening ceremony at Rushmore. Thought we might visit more than once at different times of the day.

I didn't add Wind cave, because I am slightly claustrophobic and my Hubby is just recovering from hip surgery. Thought we could handle the openess of the short Tour offered at Jewel cave.

Just a couple of thoughts--

1) Consider a visit to Storybook Island in Rapid City in addition to or in lieu of the other things you are doing. I think it's a magical place for kids, especially one that is 6 years old and admission is free. http://storybookisland.org/

2) I might skip the 1880's Train. I did this when I was a kid and I still remember how bored I was. I can't imagine it has gotten any more interesting in the intervening 45 years.

Great suggestions! I have ridden the train in Colorado-it was beautiful, however, once is enough for me. Thanks for the help.

Nice itinerary and the only remark is why Badlands to Spearfish on the last day and then back Spearfish to airport...
It will be a long drive day and there are some nice small hikes while in Spearfish around the lodge(some nice waterfalls).
I know it's difficult with reservation but as you have thinking of Devil's tower and Deadwood, I will have cut one night in your first adress and add one night in Spearfish in the end to do from Spearfish Devil's tower, Deadwood and the hikes around the lodge.
Circle view ranch is a very very nice adress...
Mammoth site is a must with child. Evening ceremony is Mt Rushmore was not for us very impressive...A minimum of a half day is necessary(the trail at the feet of the head is easy). While in Keystone the alpine slide could be cool for the child.
Reptile gardens has a lot of activity interesting also for your child.
Not sure that Wounded Knee would be so interesting for the 6 y old...(we found it interesting but we are adult...).Wall drug is nicer for him ands there is in Wall a "wounded knee memorial" which is a must on the story of the indian war.
Erik

If you edit the train ride and your little one likes dinosaurs you might look into sites in S.Dak. I see you have the mammoth site. Our grands really had a great time at near that age on a dinosaur trip we took them on.
And Wounded Knee might be over his head--but you never know. We LOVED the Badlands!

http://www.blackhillsbadlands.com/home/artsculture/museums/bonesandstones