Translation:ke kumu āna
My understanding is that "o" nouns are ones that you are born with (parents, grandparents, etc.) and "a" nouns are the ones that you acquire (children, teachers, etc.) regardless of whether they were chosen or not. Other "o" nouns include things you can wear (clothes, shoes) and things you can be in (house, room, car), on (chair), or under (blanket).