The American family has changed significantly over the past century.  If you're interested in seeing exactly how, the Marriage and Religion Research Institute has created an interactive online tool which allows users to map demographic trends over time in a variety of ways, including by US state, ethnicity and gender.  You can have a look for yourself here. 
The Institute has also published family trends, including demographic and population data, which might be of interest on their website here.  One significant trend is the huge increase in children from the 1970’s onwards who have parents who are divorced, co-habiting but not married, or have always been single; a significant change in up-bringing for a large number of children across America from that time.  For those children that live below the poverty line the trend is much worse but still begins around the same time in the early 1970's.  If you live in the US, have a look at how your state is doing on the family front.