She is such a sweetie

Me: Mackenna, Daddy is Grandma's kid.
Mackenna: No, he's a daddy.
Me: Yes, kids grow up into daddys.
Grandma: And daddys grow up into grandpas.
Grandpa: And grandpas get old and decrepit.
Mackenna: Like you, Grandpa?

And Later,
Me: Mackenna, who is decrepit?
Mackenna (without any hesitation): Grandpa!!