I took the course Writing for Children and Teens a couple of years ago. Before even completing the course, I sold two magazine articles that I had worked on with my instructor! I am currently working through their advanced Writing and Selling Children's Books course. My instructor for both courses has been Victoria Sherrow. I cannot say enough good things about her insights. Her comments always ring true and have honed my writing skills.
You can work at your own pace, with a great instructor and well-thought-out materials. If you really want to be a writer, do this for yourself!