I think they are fairly challenging reads for kids ages 7 to 9, but they should be quite manageable as independent reads for kids ages 10 and over.
If you're looking for a book with a strong female protagonist, all five of these books have one. They are great books for both boys and girls.
Charlotte's Web, by E.B. White
This is a wonderful classic that introduces young children to many deep and thought provoking ideas: the power of friendship, the cycles of life and death, the connection between humans and animals, and the idea of growing up. The narrative structure, vocabulary, and themes make it a rich reading experience for young kids.
Where The Mountain Meets the Moon, by Grace Lin
I read this book aloud to my children last year, and they both adored it. The book uses Chinese myths and folktales to weave a highly imaginative story about a young girl's quest to help her poor family. Over the course of her travels, she realizes that true treasures have little to do with money and more to do with love, family, and friendship. The book is a work of art on so many levels: it's beautifully written with vivid metaphors and rich language; it has some stunning illustrations; and it is moving and thoughtful.
Number the Stars, by Lois Lowry
This is a good introduction to World War 2 for young kids. Lois Lowry presents a compelling story about a young Danish girl whose family helps protect a Jewish family during the Nazi occupation of Denmark. Gentle, thought provoking, and well-written, the book will engage and educate young readers.
Flora and Ulysses, by Kate Di Camillo
A hilarious book about a superhero squirrel and a young, somewhat eccentric girl. The book had all of us in splits. In addition to the humor, the book examined a wide range of human emotions from fitting in to feeling abandoned.
Esperanza Rising, by Paula Munoz Ryan
A beautiful book about a wealthy, young Mexican girl who is forced to leave behind her wealth and escape to America, where she has to live as a migrant laborer. The book is great for teaching children about empathy, courage, and our common humanity. A beautifully crafted book, it will stretch young readers and help them develop their vocabulary.