There’s a big difference between picture book art and almost every other form of commercial illustration. This “thing” that sets kid lit illustration apart from most other forms is that it is “sequential” art. Like a comic book, or a rough story board for an advertisement, art for picture books shows movement along a time line.
In the development of this time line, there is also the look of the character and multiple perspectives of said character. A children’s book illustrator must be an expert at showing a consistent character in action. Which is a lot harder than it sounds. Not every artist can do this.
The ten things to show in your portfolio are:
5. Character Development and Transitions
6. Humans in other age groups besides children
7. Color and Black & White imagery
8. Sample book spreads
9. Characters in groups
10. A range of emotions