Originally Posted by
Midwest Michael
I agree with Dave, you're getting closer, but still have a couple major flaws.
The Black Hills To Coeur D Alene is more than 800 miles. That would be unwise and unsafe, even if you didn't have to think about a child. The Seattle area to Rapid City is basically at the upper limit of what you should consider doing in 2 full days of driving, and if you are going to do that, then you need to stop at the halfway point - which would be Butte, MT.
If that is the approach you're going to take, then I would strongly recommend flipping your trip around and do the long drive out to South Dakota first, when everyone is at their most fresh and energetic, rather than trying to pile 2 long haul days on the end of a still fairly fast paced trip where everyone is going to be a little tired.
I will throw one more idea out to add some variety into your trip. Rather than backtracking on I-90, you might go from the Black Hills to Cody, then to Yellowstone, and finish with Jackson/Tetons. From there, that would allow you to head west to Idaho and return via I-84/I-82, stopping in Boise or somewhere like that on the way home, without adding much in the way of travel time.