I wish the author had shown their work regarding the mother's after-tax income. They apparently assume a 22% effective tax rate, but that seems unrealistically high.
The SSA says that Social Security tax was a mere 1% before 1950, and would remain below 4% until the 1970s. [1]
A 1949 Form 1040 [2] suggests that a single filer with 3 dependent children, earning $2700 that year, would have a federal income tax liability of only $7. Not 7 percent, 7 dollars.