pi r square

I have taught my Gr. 7 Math tutor student about circle a while ago. Now her school finally goes over it. In order to show that she still remembers the formula in front of her mother:

me: What is the circumference of the circle?
L: you times 2 times radius times 3.14.
Me (tries to explain to L's mom): That means "2 pi r".
L's mom (looks puzzled): isn't it "pi r square"?
Me (asks L): What is "pi r square"?
L: Area!
L's mom: LOL! That's why we have Mandy here!

I think L is so glad that she knows sth that her mom doesn't know.
I am so happy that she remembers sth and begins to like Math.