Here is the submission website for Charlesbridge. They publish wonderful children’s books.
http://www.charlesbridge.com/client/client_pages/submissions.cfm
My best advice, that I also need to take, is to read, read, read children’s books. We learn from all of them.
I have had many non-fiction articles, with my photographs, published in children’s magazines and a few books. I love non-fiction writing, but poetry and fiction are important to me too. What do you like best? Read and study and read more, the magazines and books you’d like to be published in.