Precious to me: Once a upon a time...

Once upon a time, a little girl, K, loved reading bedtime stories before going to bed. Her mommy and daddy loved listening to her start the story in her little girl diction... She always started stories with "Pan-a-pan-a-time...." This made her mommy and daddy smile.
K is now 3years old and last night, while reading a story, daddy started with, "Pan-a-pan-a-time...." To which she replied, "No daddy, it's once upon a time."
Oh dear, for while mommy and daddy are proud of her, it leaves a little twinge on her mommy and daddy's heart to see her growing up so fast.