The illustrator is Deborah Niland. She illustrates a lot of children books. I really like the naif style of each of her illustrations as well as the reach amount of bright colors. Every illustration has a magic and worm atmosphere, appropriated for the public the illustration is made for, children. Here i leave a link to her web-site which as a children atmosphere that I've founded very interesting.
http://www.deborah-niland.com.au/index.htm