It's about integral development of a person, and as Pope Blessed Paul VI said:  " Man is not really himself, however, except within the framework of society and there the family plays the basic and most important role. "

And "The natural family, stable and monogamous—as fashioned by God (37) and sanctified by Christianity—"in which different generations live together, helping each other to acquire greater wisdom and to harmonize personal rights with other social needs, is the basis of society" 

And " In the task of development man finds the family to be the first and most basic social structure"

thanks.