Montana is a western state with a diverse terrain ranging from the Rocky Mountains to the Great Plains. Take the kids to see the pristine wilderness and awesome wildlife.
A couple of fun destinations are:
1. Glacier National Park
Drive the Going-to-the-Sun Road that goes up the edge of the mountains and crosses several waterfalls.
The only year-round entrance to this national park is in Montana. The Roosevelt Arch in the town of Gardiner welcomes you and a few of the activities available are rafting, hiking, and horseback riding.
More information is here