In its quest to make information equally available to everyone, the Library of Congress has digitized books that were published over 100 years ago and made the collection available to the public online. The site explains, “This special collection presents children’s books selected from the General and Rare Book Collections at the Library of Congress.”
However rare, many of the books are still widely read today, such as The Secret Garden, and The Arabian Nights. These books are now in the public domain, and you can use them as freely as you like.
Access the entire collection here: https://www.loc.gov/collections/childrens-book-selections/