The Birchbark House, by Louse Erdrich- similar to the Little House series, but through Native American (a young girl's) perspective
The Light in the Forest, Conrad Richter- about a white boy rised by Native Americans
Code Talkers- my be too "old" for age 7, about Navaho people who used their native language for coded messages during WW2- great read, more modern take on Natvie American assimilation, loss of tradition, etc.
Cynthialeitichsmith.com has some good resources for children's and YA books and Native American authors
