Books for 4 year olds are written both to be read to a child and to read with a child. Phonics and sound patterns linked to reading are started as part of school learning for 4 year olds. Repetitive and rhyming words and sounds are useful to help with this.
Stories and characters to help teach empathy are also common in books for 4 year olds, as part of emotional learning. If you're just looking for a good story, recommendations from your own childhood, from friends and family or from a bestseller list are brilliant.