The Price of Motherhood
"...So, if you have your first child at 24 instead of 25, you're giving up 10 percent of your lifetime earnings. The wage hit comes in two pieces. There's an immediate drop, followed by a slower rate of growth—right up to the day you retire. So, a 34-year-old woman with a 10-year-old child will (again on average) get smaller percentage raises on a smaller base salary than an otherwise identical woman with a 9-year-old."