Academic Search Complete provides a variety of information about children's books. Includes reviews, articles about teaching using children's literature, author's insights and interviews, almost anything!
Children's Literature Comprehensive Database provides access to a wide range of reviews and other information related to children's books. Great resource.
First Opinions, Second Reactions a free online journal that offers reviews of children's books, aimed at K-12 teachers, parents, librarians and children
Children's Literature Comprehensive Database lots of reviews and can search and narrow by a variety of factors: Reader's age, Grade level, fiction or nonfiction, genre, accelerated reader points, reading level, and many others.