age confusion

We have a sweet friend, Christi, from Birmingham who has decided to come live with us this year. She works with me in the mornings teaching the kids as a way to cover her room and board. Having her here has been an amazing blessing to our family and to my sanity.
The funny thing is that the kids can't quite seem to grasp what age category to put her in. They have made some really funny comments that I've been meaning to share.
One morning she was helping me load the kids in the car and Oliver asked her, "When are you going to have a baby?" She started laughing and tried to explain how she would prefer to have a husband BEFORE having a baby. Then as a follow-up question as we were leaving her, he asked, "Are you allowed to stay home by yourself?" revealing his uncertainty to her age. I guess she is allowed to get pregnant, but not stay home alone. Nicholas tried to explain to Oliver that if someone was old enough to drive a car, then they are old enough to stay home alone. His explanation seemed logical enough.
Just the other day, Oliver was looking in Christi's room and saw her "Lord of the Rings" trilogy. He suspiciously asked, "Are you old enough to watch that?" I guess he just can't decide whether she's a child or adult.