When looking for children's book reading levels, trusting sites such as Barnes & Nobles and Amazon are not necessarily the best places. Using more authoritative sources who employ children's literature and reading experts, is a more reliable choice. Book reviews can help you select appropriate books by giving you a brief summary of the book, a genre(s) description, and some give reading levels.
School Library Journal has been reviewing children's literature for decades. We have access to SLJ from 1970-Current in the database Academic Search Complete. You can use the link below to Swoop Search and follow the instructions on searching. If you can not find your title or if your book is published before 1970, just let me know and I will help you find the review.