How Mountains Are Made by Kathleen Weidner Zoehfelt (illustrated by James Graham Hale; Harper Collins, 1995) is a Lets-Read-and-Find-Out book (Level 2). The books in this picture book informational science series are sometimes uneven, but this one hits the mark for teaching many concepts with a friendly frame.
In How Mountains Are Made, the facts about how mountains develop and change are shared in the context of an illustrated story of children going for a hike in the mountains. The children find fossils, and this begins an explanation of how the land has changed over time. How Mountains are Made gives great details on the various ways mountains can form. (For teachers and homeschool parents, I recommend the “towel” activity on page 18 to introduce mountain formation to your students.)
