Another Jessicaism

My daughter has two cousins – sisters – who are very close in age. They get to see one-another several times a year, and my daughter is getting to be pretty good at general observation.
I guess the girls were arguing about some trivial detail – as sisters close in age are wont to do – and my daughter walked out of the room.
“All they do is fight,” she said.
“Yes, they do,” my sister-in-law responded.
“I guess it’s because they’re premature,” my daughter said.
My sister-in-law had to leave the room before busting up.
“I didn’t have the heart to tell her it was the wrong word,” she said.