Family Leave

The USA is among the worst of all nations when it comes to mandating family leave upon the birth or adoption of a child. See for example http://www.huffingtonpost.com/2013/02/04/maternity-leave-paid-parental-leave-_n_2617284.html
What are the benefits (developmental, social, economic, etc.) for the family and society of a government- or business-sponsored plan to provide leave for family members? What are the best arguments we can make to our legislators to enact swift implementation of The Family and Medical Insurance Leave Act (FAMILY), as introduced to Congress in December 2013 and already well-established in some states like California?