I'm often asked how to get started writing for young readers. In addition to my answers HERE, I suggest joining the Society of Children's Book Writers and Illustrators, an international organization with conferences worldwide. Attend a conference for your local chapter or region, or one of SCBWI's two national conferences held each year. For writers on the U.S. East Coast, I also recommend Rutgers One-on-One. For constructive editing, encouragement, and all-around help moving forward with your work, join an in-person or online critique group. And check out Jane Yolen's famous "BIC" and other good advice in this WRITER'S FAQ.
Excellent books about writing abound. BUILDING FICTION by Jesse Lee Kercheval is the nuts and bolts book about craft that I recommend to my students and manuscript-editing clients, and to published writers at any level of experience.