boob milk.

"Mom, when the baby is born, are you gonna feed it milk from your boob like you did with Adley?"

Boobies.

Kenley "Boobies is big."
Me: "Whose?"
Kenley: "Your boobies, mom."

Boob Diaper.

*Kenley hands me a nursing pad*

"Here, mommy.  Here's a diaper for your booby."

Boob Feeds.

Kenley: "I gotta go potty."
Me: "Hurry up, your sister's hungry."
Kenley: "You gonna feed sister Adley with your boob?"