I mean, it seems obvious to me that the paintings in my books are famous, and that I didn't paint The Starry Night or The Scream myself. But to a child, who doesn't understand the whole bookmaking process, it only makes sense that if my name is on the cover, then I must have made the pictures inside. So I go on to explain that these are photographs of paintings that hang in museums, and that I have to get the museum's permission to use these paintings in my books.
But one of the cool things about this question is, it made me think differently about my books. After all, how many authors can say they've written a book illustrated by Jasper Johns? Or Pablo Picasso? Or Leonardo da Vinci? I actually have the privilege of working with some of the finest "illustrators" the world has ever known. I even have the power to choose which ones I want to work with. I can "hire" whomever I want.
So in a way, I am doing my own illustrations. I'm able to look at the entire history of art and choose whichever pieces I think best illustrate the story I'm trying to tell. The creativity comes in the choosing. And so does the fun.