Three or Thirteen

Is my daughter really only three?
We went to the optometrist for an eye check up. While we were waiting for the doctor to come back in she informed us that we needed a check up and that she was the doctor. My wife went first. She received a thorough exam complete with pictures of her insides. K has never even gotten an X-ray before!?
After completing our exams we were looking at pictures on the wall and found some dolphins. K said "Dolphins aren't fish Dad, they're mammals". That's right, my Three year old said that. I looked at N and she looked back at me as stunned as I was.
I guess I better go study now, so I can stay ahead.
Proud father.