You'll ALL enjoy the trip. In Coeur d'Alene we usually stay at the Elks Lodge but that might not be suitable with the two little ones. My next choice would be Blackwells. Clean campground with boats for the kids to watch. Jellystone is a good choice in Missoula. We stayed at Three Forks and they have a bakery to die for..:)...Our choice for CG in the Mt. Rushmore area would be Rafter J..especially with the kids. Custer's isn't bad either, but we preferred Rafter J.
Yellowstone is a figure eight, with the upper circle having more animals and the lower circle containing Old Faithful and most of the geyser activity. Early morning or dusk is best time for animal viewing. Bison are out everywhere all day. We liked Grizzly RV park outside the west entrance. The city is within walking distance of the park for eating and shopping. Lots for kids to do there too.
Enjoy the trip...Dennis
Yellowstone