Read as many children's books as possible. This is good research to help you assess what publishers may be looking for. Reading other children's books may provide you with ideas for your book.
Furthermore, read children's books that have been published recently. This may help you identify potential publishers of children's books that have a similar style to yours.
Research publishers' websites. Search for publisher submission guidelines. Discover what types of children's books are most often published.
Always submit your best material. You may need to make several revisions before you're ready to submit your children's book or song to a publisher. Read your submission aloud, at least three times, to make sure it "sounds" correct.
Have someone, preferably a fellow writer, proofread your manuscript for errors. Consider joining a focus group to receive feedback and a professional critique of your children's book. Make your final revision after you've edited your manuscript and have had it reviewed by one of your peers.
Present your formatted manuscript in a professional manner. Publishers have no shortage of manuscripts to review. It's highly unlikely any publisher worth its salt will take the time to consider a manuscript that hasn't been properly prepared.
You can learn to properly format your manuscript at websites like writing-world.com.
State your submission status very clearly in your cover letter. Some children's book publishers require an exclusive submission, while others allow multiple submissions.
An exclusive submission means you can't submit to multiple publishers. Multiple submissions means you can send your submission to as many publishers as you want.
Include a self-addressed stamped envelope with your submission so your manuscript can be returned to you. Be sure to send only one submission per publisher, unless a publisher has specifically requested otherwise.
Keep file records of all correspondence.