babies swimming
Toddlers explore the water with their mothers during a swimming class for babies at Lane Cove pool February 16, 2007 in Sydney, Australia.
  • America's shrinking birthrate is a problem.
  • Millennials not having enough babies could crimp growth by 1-2 percentage points a year.
  • At the current trajectory, that's set to weigh on the economy for the next decade or more.

Millennials aren't having as many kids as previous generations, and that fact could end up dragging down economic growth for more than a decade.