Whitman, for example, releases many concept-type books while Green Tiger Press books have a dreamy almost metaphysical quality. One of the best ways to learn the ins and outs of the industry is by joining the Society of Children's Book Writers. They are probably the best known professional organization for writers and illustrators. Their quarterly newsletter is filled with everything from editorial updates to short inspirational articles. The Society of Children's Book Writers can put you in touch with other children's book writers and alert you to conferences in your area.
Conferences can be a good initiation.
One of my favorite conferences was the Port Townsend Conference in Washington state where I wrote, critiqued, and studied with Jane Yolen for ten days . Attending the American Bookseller or American Library Association conferences are a great way to take stock of what's in the market place. I'll always remember editor Kathleen Krull talking about how she judged a children's book contest. She separated stories into three piles of possibility and then decided to analyze what made a manuscript worthy of winning. The one quality that ran through the manuscripts she considered most carefully was originality.