A good description of the changes in American families from 1910- 1990.

For example, see this figure for how fertility has changed over the 20th century.  The number of children per family declines until after WWII, then increases dramatically until it reaches 3.7 children per woman (family) in the late 1950s, (higher than in the 1920s), then declines again in the earlier 1970s to less than 2 children per woman (family).