What holds this floor up?

Alex: You have a brown shirt on, Mommy.
Mommy: Yeah.
Alex: Why?


Daddy: Hey Alex, I'm gonna go get a haircut, so I'm gonna give you a kiss now, okay?
Alex: Okay.
(Daddy gives Alex a kiss.)
Daddy: I love you.
Alex: Bye. What are you gonna watch there?


Alex: That's amazing.


Alex (looking out the front window at a boy riding in a wagon): He's riding in a wagon.
Mommy: Yeah.
Alex: Why is he riding in the wagon?
Mommy: Because his daddy wants to pull him in the wagon.
(Alex watches a bit more.)
Alex: One day can I ride in the wagon?


Alex (flipping coasters): Mommy cooks dinner, Daddy sits on the couch, Alex goes on the stool, and Claire goes on the chair.


Daddy: You're a cute boy, Alex.
Alex: Thank you, Daddy.


Alex: But daddies don't have a tray. They can get down by themselves.
Daddy: Yeah, daddies don't have a tray.
Alex: But kids do. And sisters and brothers.


(upstairs)
Alex: What holds this floor up?