I think they state single mothers because the assumption is that a single father is a widower and that the children were born in wedlock. Also it is less common. But there is no reason that has to be true. However, following the widest version of it also includes anyone that has every had any form of premarital sex.
I think they state single mothers because the assumption is that a single father is a widower and that the children were born in wedlock. Also it is less common. But there is no reason that has to be true. However, following the widest version of it also includes anyone that has every had any form of premarital sex.