Two Little Girls = Hilarious Conversation

As you may know, I babysit in my home to help make ends meet as well as work in the Rec Center's Day Care one morning a week. I have a sibling set, Emmy and Reed, who come everyday but Thursdays and then three others who come less often. This week I have had my niece, Kelsey, with me while her mom does some substitute teaching.
This morning Kelsey wanted some toast. As I placed the toast with it's butter, sugar, and cinnamon on it, she is a very specific little lady, in front of her she said, "Thank you, Julie and Happy Holidays!"
Later during lunch Kelsey told Emmy that there were cookies for after lunch. Emmy asked me if I made them last night. I told her that Kelsey brought them to share with us. Emmy turned to Kelsey and said, "Thank you." Kelsey smiled and said, "Happy Holidays."
While they ate I was cleaning out a portion of my cupboard that hold the Campbell's soup labels that I have saved. I decided to cut the little UPC coupon part off rather that store the whole label and keep them in a little baggie. It took all my concentration so I didn't hear the whole conversation going on behind me but when I did tune back into reality this is what I heard:
E: I would like to marry him but I can't because we are brother and sister.
K: When you grow up?
E: No, when we grow up we will still be brother and sister, we will always be brother and sister.
K: Oh.
I snickered to myself.