What Is This?

One of Elias and Micah's favorite read is The Big Red Barn. This is what happened one night last week just before bedtime as we're reading it:

E&M (pointing at the cows' udder, wanting to know what it's called.)
K: udder.
E&M: udda
K: only mommy moo moo has udder
E&M: mommy udda
K: no, mommy don't have udder... mommy cow has udder.
P: LOL as he rolled onto the floor.
E&M: mommy udda
K: mommy COW has udder
E&M: mommy moo moo udda.
K: yes, good job boys (I was dying inside...it's too funny LOL)