My DD loved The All of a KInd Family series at that age, especially because the youngest sister was also 4 in the first book. Same with the first in the Ramona series. She loved having a character her age. I strongly second the Shoe books. They are really wonderful. Charlie and the Chocolate Factory, James and the Giant Peach and Peter Pan were also big hits. We waited until she was 7 for the Harry Potter books but then they were huge favorites. I I would not have been comfortable doing them with a 4 year old.

If you are reading aloud you can still do some editing if needed. We went through a lot of the classics on audio books but there is a lot of racist language, death and violence it would have been nice to edit out if we were reading them aloud instead. Especially Doctor Doolittle.