Seeking advice for Mt Rushmore area

I am planning to knock Mt Rushmore off of my bucket list in about three weeks. I am flying in to Rapid City with my 18 and 8 year old...then hotel staying (not camping).

We plan to see Rushmore, Crazy Horse, Custer State Park, and Devils Tower. I am asking for everyones advice on must see/do things while we are there, as well as fun things to do with the kids.

Any oddities that aren't in the travel brochures are good too.

Thanks