I have done the Yellowstone/GT/Rushmore loop twice now, with children (ones that like camping and hiking mind you) as well as 4 other trips to Yellowstone/GT
Split of 5/2 between Yellowstone and GT is about right. We would arrive midday, see the sights, book a float for first thing the next morning (early = more wildlife) then head north to Yellowstone.
Rushmore is a one day, see it as you are driving by. Yes there are more touristy things to do, but I would do a day tops there. Better to break the drive to Rushmore into two days and take in Devils Tower. My favorite stop over in between is the Bighorn Mountains. More of a plateau, but very scenic. Have always wanted to go there for several days as a destination.
Regarding Craters of the Moon? I enjoyed both visits, spelunked a couple wild caves there in my youth. Cutting short the tetons by a day and going out there would be fine. As would a detour to Mesa Falls, just to the SW of yellowstone. Incredibly scenic black volcanic rock falls.
If anyone in the family is a western history buff, spend the better part of a day at the buffalo bill museum in Cody as you exit Yellowstone, on the way to Rushmore. You can't do it all in a day, but you'll get much of it.
Your 5 days in Yellowstone will not be enough to see everything. I've now been there 6 times, 33 days, and I still saw stuff I hadn't seen before when I went last summer. But you'll get a great sampling of the park.
