One of the best places to get free books is also a place to donate books. Many “Friends of the Library” Organizations take used books and sell them to help them raise money for library operations.
Little Free Libraries is a “take a book, return a book” free book exchange. These adorable libraries are popping up all over and are a great place to donate your books.
Ask your local shelter or food bank if they take donations of used books. Specifically used children’s books may be well received by those utilizing these services.