http://www.equality-of-opportunity.org/
Likelihood of a child born in a given year eventually earning more than his/her parents at age 30 (inflation adjusted):
1940 91.54%
1945 86.42%
1950 78.51%
1955 69.64%
1960 62.33%
1965 59.33%
1970 60.95%
1975 58.59%
1980 50.03%
1984 50.26%
Of course, the parents of the earliest cohorts were working or unemployed during the Great Depression, so the depression of their earnings made it easier for their kids to do better. However, the trend is still downward even after the period where one’s parents were adults during the Great Depression.
The next chart below shows that, for those born in 1940, only those born to the top 1% had a less than 50% chance of exceeding their parents’ income (41.1%). But in 1980, those born to the top 67% were more likely to be downward mobile than upward mobile in an absolute (not relative) sense.