In the car, on the way to preschool

Gwen: Mom, what are those pink things on the ground there?
Me: Remember when the trees all got flowers on them?  Those are pieces of the flowers that have been blown off the tree by the wind.
Gwen: Why do they blow down?
Me: Well, in the springtime, the trees all get flowers - those are called blossoms.  Then at the end of spring, the wind blows them off the tree to make room for the leaves.
Gwen: I wonder when my apple tree will get flowers!
Me: It might already have flowers, actually.  We should look when we get home.
Gwen: I meant apples.  I wonder when it will get apples.
Me: Apples come in the fall.
Gwen: Is it fall?
Me: No, it's still spring.
Gwen: It's my birthday.  My birthday is in spring, and it's still spring, so it's my birthday.
Me: Your birthday is only one day.  Spring is a season that lasts three months.  Do you know what birthday means?
Gwen: What?
Me: It's the day when you came out of my tummy and into the world, and were a baby.  It's the day you were born.  It was only one day.
Gwen: But it's the day when you turn older.  I was three and then on my birthday I was four.
Me: Yes, that's true.  Your birthday comes every year, but it's still just one day every year.  When you were one, it meant that you had been ONE YEAR since you were born.
Gwen: Mom, let's stop talking about birthdays now.
Me: Okay.