I just stumbled across a website called Author Tracker. Heard of it? You can find your favorite authors and sign up to have email notifications sent to you when they have a new book ready to hit the shelves. Author Tracker is searchable by author/illustrator name, book title, or subject, and they have an entire section devoted to children's books.
The only downside is that it's not entirely author-comprehensive, but limited to authors who are published with Harper Collins. Still, there are lots of familiar names to choose from, including Meg Cabot, Beverly Cleary, Kevin Henkes, Jean Craighead George, Shel Silverstein, Arnold & Anita Lobel, Patricia MacLachlan, Jack Prelutsky, Maurice Sendak, etc.
Now, I'm not sure how helpful the email alerts will really be (what I was looking for was something more comprehensive about future releases in children's books) but I may sign up for a couple and see if it's worthwhile. Just thought I'd pass along the link in the meantime.