Here is an interview with Ronald Searle that is definitely worth watching. Ok, so he isn't exactly in the category of 'Children's' Picture books, but he IS in the category of Picture books for grownups and Comics and so as you know the connection in terms of process and artistry is obvious.
My favorite bit he says in the interview, regarding his work: ' The moment it's successful- kill it! Because it can only get worse from there.' That strategy towards your work really shows artistic integrity and is sooooo very very sadly hardly existing anymore in our current age of making a series out of everything in order to sell the sticker book, stuffed animal and mug to go along with your book.
Also, noteworthy other than the fact that Searle appears to be drunk at all times, is his desk of which you get a really good long view during the interview. Notice the color-coded planner and the many small timers hanging up. Timing yourself for drawings can be a really great and effective way to work! But yeah, this man totally rocks! Check out his stuff if you're not familiar with it because he is one of the great masters of visual slapstick and comedy! Yup. So good!