Twice a year Publisher’s Weekly puts out a specific issue geared solely for the children and young adult markets. It’s an excellent resource to study publishing houses and new trends. Check out your local library for a copy of the most recent edition. Note which books grab your interest and why and write them down in your idea file, or reading file.
However, also remember that the market changes at a rapid pace, so it’s more important to find out what age and genre and topic you love rather than follow trends, which can change in an instant.
Picture books: Tend to separate into two main categories age wise. Ages 3-6 are predominately the more familiar versions where the author and illustrator’s talent merge to create a visual and auditory voice that invites their readers into a new experience.
Storybooks lean more to the 4-8 year olds and are heavier in text with illustrations that maybe highlights as opposed to integrated storytelling—basically both text and illustrations could stand on their own. However both categories also intermix across all ages, which can add a little confusion.