Young children do take a toll on work. The paper found that there is a 15 to 17 percent drop in productivity among women with little kids. For those with multiple children, the first child results in a 9.5 percent drop in performance, the second child cuts out another 12.5 percent and the third child caps it off with an 11 percent decrease in productivity.
In other words, three preteens will result in a 33 percent loss in productivity on average, the equivalent of four years of research.
But as any parent knows, the days are long and the years are short. That’s the case here, too. Mothers tend to be more productive both before and long after the birth of their children. When that work is smoothed out over the course of a career, the paper found, they are more productive on average than their peers.

“While you have small children, it has an impact on you,” said Christian Zimmerman, one of the paper’s authors. “But after that, it seems that the impact is the other way.”