Oh, SO glad that someone mentioned Magic Tree House. DD devoured those when she was about five. She also really liked the DK Eyewitness books and Magic Schoolbus.

Another set of books that my DD was very fond of--

the Frances books,

the Little Bear books.

She also REALLY loved all of Jan Brett's books at about this age-- the illustrations are lovely and intricate, and there is a considerable amount of text on each page in some of them.

Schrödinger's cat walks into a bar. And doesn't.