I think you might have misunderstood the suggestion. Giving people enough time to manage a family is different from giving more time to people who have families.
An employer might prefer having employees with children for a variety of reason and mostly would treat "family benefits" as method to hire older more experienced people.
> it's illegal to even ask if people have children in interviews.
This is to avoid so discriminate against people without children, an objectively right objective.
Still you can accommodate the needs of people with children as a sort of "levelling the field". The same way you can accommodate the needs of minorities by making sure that office culture is respectful of their identities.
If I can go a bit off-topic in both cases the specific demography you are trying to help might be just an example of a common human trait that is just easier to see in some people. Sometimes single men want to work part-time and white rich people do not like racist jokes.
An employer might prefer having employees with children for a variety of reason and mostly would treat "family benefits" as method to hire older more experienced people.