When my son was in the 2-7 age range, we used our library extensively. I took him to the library once a week or once every other week, and just let him roam among the shelves and pick books that he wanted to borrow. We sometimes borrowed 40 books at a time... I think at this age reading a variety of books is great because there is so much they can discover through books. I honestly didn't think about reading levels at all. Books that the kid wants to read and can understand are definitely at his level.
We also asked the librarians to help. Just told them what books my son had enjoyed, and they rattled off a long list of similar books.
