Early readers as a genre have controlled vocabulary, sentence length, and structure to make them accessible for children who are just learning to read. It’s tricky for an author to write within these limitations and still create a good story, but there some great examples.
The first book I ever read by myself was Frog and Toad are Friends by Arnold Lobel. I was SO proud!
I then went on to read the Little Bear books by Else Minarik, illustrated by Maurice Sendak. I especially liked the story about the mermaid.