If you write picture books, you've probably thought at some point, "Boy, it would really impress the editor if I hired someone to illustrate this book. Then it'll look like a real book." But really, that's not true. The publisher wants to hire the artist.

They want to choose an artist whose style they like-- possibly someone they've worked with before, possibly someone who's won awards or has a great track record. They'll want to enter into a contract with the artist for the rights to the work, and give specific direction for page counts, style, colors, size, etc.

If you're a professional artist yourself and want to illustrate your own books, sure, submit it as a complete package-- but otherwise, don't hire someone or enlist your cousin or son (who's undoubtedly talented, but likely not what the publisher is looking for).

It will more than likely count as a strike *against* you to submit art with the writing. It brands you an amateur. Some publishers are more than happy to hear your suggestions once they're considering buying your book if you've come across an artist whose style you think fits the book. But before then, don't waste anyone's time or your money.