We do see that there is a family gap between women with children and women without children. Women with children earn less, even after controlling for work interruptions. Some estimates suggest that these earnings losses could be as large as $11,000 in the first year and maybe $8,000 in the second year. The break-even point is around seven years after a child is born. As you can see, we do have information about the impact of children on earnings.
We also have information on what happens when a woman delays having children until she is a little older. We know that at the beginning is when lifetime earnings grow very quickly. You accumulate more work experience and training, so depending on when you take time off to have children, it may have an impact on your wages, and that may carry through over time.