Don't read a book Mom, ask me!

How do you explain to a child what you do to get a PhD?
Phone conversation:
"Hi Mom, how are you? What ya doing?"
"Well sweetie, your Mommy is studying quite a bit and does lots of homework."
With concern in her voice, Valerie queried, "How can you still be in school when you are as old as you are?" (probably beginning to wonder if Mother had been held back for many years and was repeating a grade....)
"Well, Valerie, learning is a life-long process, you don't stop learning just because you graduate from High School."
"Hmm. I don't know if I want to keep doing homework the rest of my life," she said with a worried voice. "What are you studying about Mom?"
"Well, interestingly enough we are studying children and how they grow and develop."
"Silly Mommy, you don't need to read a book about children, just ask me. I'm a kid!"