We say bottom, not butt

This is a coversation we had in the car on the way to school today.

Brax - Mommy, we say bottom, not butt.
Brecca - Mom, Brax said butt!
Brax: I say bottom, not butt.
Brecca: No, you said butt.
Brax: Mommy, Di di (Brecca) say butt.

Finally I had to intervene!

Me: OK, we don't say butt. Nobody in this house says butt. So both of you, quit saying it!
Brax: Hey Di di, Mommy say butt. We don't say butt!