The American Sociological Association's researchers Roberta Spalter-Roth and William Erskine did a study of which sociologists use family-support policies, such as flextime and delayed tenure clocks. They wanted to see if mothers were more productive than their childless counterparts when they used such policies.
The results are striking. Mothers, not surprisingly, used family-support policies much more than childless women do. And it is also not surprising that mothers who didn't use family support were less productive than childless women. Thus, in 2003, these were the median number of peer-reviewed publications for the two groups:
unsupported moms: 4
childless women: 5
And now comes the interesting part. Family support closed the gap between moms and single women. And then doubled the gap, in favor of the moms. Average number of peer-reviewed publications by supported moms: 9.
Having kids is not career death for academics. On the contrary, with a bit of support from the school, mothers can be much more productive than childless women, just as fathers have long been more productive than childless men.