Right in the heart of Missoula is an old-fashioned carousel that is not only fully operational, but is very inexpensive to ride. If you're on a family road trip, the kids will love it. The whole area is a fun place with parks and river walk and lots of shops and restaurants.
If you go:
This would make a great 'rest stop' for you, even if you aren't staying in Missoula. It isn't far off the interstate, and the whole family can enjoy it.
Links:

101 Carousel Drive
Missoula, Montana 59802 USA
Mailing address:
A Carousel for Missoula
101 Carousel Drive
Missoula, MT 59802 USA
Phone Numbers:
Carousel for Missoula
+1 (406) 549.8382
+1 (406) 549.8382