I love children's picture books (ehon). Since Japanese children's books are usually written in hiragana only, I think it is great material for a learner to practice their Japanese reading with. However, I understand it is hard to purchase "ehon", and they can be very expensive, unless you are living in Japan.
"Ehon Navi" is an information site for children's books. It has been my favorite site for long time. "Ehon Navi" provides a great service, which allows a viewer to read books online. They have more than 600 books available to read. There are a few rules: You need to register (no fees) and sign in. Also, you can read each book only once. Even if you don't feel comfortable about registering with the site, you can still access more than 6,000 books in a different way. You are not given access to whole pages, but you can read what is offered from each book as many times as you wish.
I recommend that you check out this generous service. I believe it is a fun and effective way to learn Japanese, especially for intermediate learners.