"‘I told her they had used a brown man’s sperm.’ "
I don't know how mixed race families teach their children to deal with questions but a six year old talking about a brown man's sperm vs. daddy's sperm freaks me out.
I remember an episode of Lassie where Timmy is at the table with Mother and Grandpa explaining what he learned about making tadpoles. He said the male spreads his milt over the eggs and Mother and Grandpa look at each other.
It is strange, and a bit disturbing. When I was six I doubt if I knew what sperm was. Also, kids that age don't notice race unless some racist adult makes a big deal about it in front of them.