Highway Traffic Safety Administration warned that the problem could make it "difficult to remove the child from the restraint, increasing the risk of injury in the event of a vehicle crash, fire or other emergency."

"Some of these consumers have had no choice but to resort to the extreme measure of cutting the harness straps to remove their child from the car seat," the NHTSA letter said.

The recall covers 11 models made from 2009 through 2013 by Graco Children's Products Inc. of Atlanta, and includes Cozy Cline, Comfort Sport, Classic Ride 50, My Ride 65, My Ride 70, My Ride 65 with Safety Surround, Size4Me 70, My Size 70, Head Wise 70, Smart Seat, Nautilus 3-in-1, Nautilus Elite and Argos. It's the fourth-largest child seat recall in U.S. history, according to the National Highway Traffic Safety Administration, the government's road safety watchdog.