Earlier quoted context omitted.
Fathers can be around without being married to the mother.
Yes. Do you really think most unmarried families have both mother and father in the household, though? Regular contact with the father would be a lot more difficult if he's not around except on weekends.
There's no reason for an indirect proxy when the actual figure of interest is available:
https://www.census.gov/newsroom/press-releases/2016/cb16-192...