There are several publishing terms used to categorize children's books. Picture books are generally written for very young children. These books may have only pictures or pictures with few words, or they may be nursery rhymes. Easy readers are meant for children ages six to eight who have just started to read by themselves. Middle grade books are more complex than easy readers. These books have a plot and the story usually revolves around a main character or several chief characters. Young adult books are for children ages 12 and above. Some publishing houses prefer young adult books geared toward trends while others accept young adult books that address concepts of values and integrity, or the struggles teenagers face.
After you have categorized the kind of children's book you have written, the next step is to find publishers. The only way to do this is through old-fashioned research. Go to a library, bookstore or the website of children's book publishers. Study their published children's books and find out if your book can fit into their style of publishing to reduce the likelihood of your manuscript being rejected. Study the publisher's author guidelines for submitting manuscripts to find out the exact type of children's book that publisher accepts.
Most big publishing house do not accept unsolicited or unagented manuscripts so you have to know whether the publishing house to whom you plan to send your manuscript requires an agent for submission. Smaller, independent book publishers are more likely to accept unsolicited manuscripts from unagented writers. However, most independent publishers do not have the same budget as well-established publishers such as Random House and HarperCollins and may not be able to offer the kind of advance that established publishers can.
Some publishing houses do not accept simultaneous submissions. This means they will not accept a manuscript that has been sent to several publishers at the same time. Another issue is illustration -- some children's book publishers prefer to use their own illustrators and may not accept a picture book that is accompanied by illustrations. Be sure to follow each publisher's guidelines for submission.