The Chronicles of Narnia, by C. S. Lewis
I grew up with these books, and I love them all. I can still remember reading them with my parents when I was little, especially The Horse and His Boy. As a fantasy writer for children, it’s impossible to ignore Narnia. Lewis created a deep, interesting world into which generations of children have wished they could escape–something few authors achieve.
While I do find the world building a bit thin and lacking some organization in some iterations, these books are classics for a reason. I never hesitate to recommend them.