My answer on Quora: Do the children of math teachers always pass algebra?
I do not wish to generalise, and I do not know statistics on this specific issue, but I see some reasons for children of mathematically educated people be a bit more confident in their mathematical studies at school. For example, they have never seen emotions of fear, or dislike of, mathematics in their parents. It is not about genetics, it is about inheriting certain social / cultural capital: values, habits, motivation. I intentionally avoid the word “intellect”, this is not about intellect either.