That is a rather difficult question to answer seeing that there is no specific range that is standard. It can be as little as $0 and as much and several $100,000’s or even more. It all depends on the artist, the artist’s circumstances; the demand of the artist’s work or style, and the list goes on. Seeing that illustration, especially children’s book illustration, is a freelance type of career, it is very common that illustrators will have a full time job as their main source of income and then take on freelance illustration jobs on the side.
Granted, there are some very successful illustrators that make a very lucrative income. Some even book out years in advance when taking on new projects due to the high demand of their work. Looking at artists like Chris Van Allsburg, who has made a very lucrative living of his illustration work, one might think that being an illustrator is a way of making a lot of money. Even though this is a possibility, one must realize that this not the norm.