Do not finish that artwork. If you’re an illustrator as well as a writer, submit a full sketch dummy of the project and only one or two sample finished pieces (as pdfs or photocopies, not original artwork) to showcase your artwork. Also be prepared to show a full art portfolio upon request. It’s almost certain your acquiring editor and book designer will have some revision suggestions for the illustration dummy, just as they would for the text-only manuscript. If you’re not an illustrator by profession or training, don’t submit artwork at all; the manuscript will be matched with an illustrator by your acquiring editor. Artwork that’s less than professional or in any other way not exceptional can hurt a submission by creating a negative impression. Writers who are not also illustrators (a category that includes me) must trust someone else to do the visual storytelling.