I stole this from my friend Kerry's blog (visit her at Windmill Watching). Thanks, Kerry! This says it as well as anything I've encountered.
“Many people believe that authors of children’s books eventually ‘graduate’ and go on to write books for adults. That’s like saying your pediatrician may get good enough to, one day, be a doctor for grown-ups.”
from Joy Feldman, author of The Gollywhopper Games