The End of Oz, by Danielle Paige. It’s a Young Adult Book, the fourth in the Dorothy Must Die series, but it’s great as far as story re-imaginings go. (This one being The Wizard of Oz, obviously.) My son is 4 and he actually loves it when I read it aloud.
My kids that are 7,5, and 4 love the elephant and piggie books by Moe Willems. These are especially a favorite of my two younger kids. They are pretty funny and they teach some good lessons too. My older son who is reading short chapter books loves the Magic Bone books and Magic Tree House books.