DETROIT >> The federal government’s road safety watchdog is ordering child seat maker Graco to explain why it didn’t include 1.8 million infant seats in a recent recall for faulty buckles. The company says it will comply with the request.

The National Highway Traffic Safety Administration said Friday that Graco has until March 20 to explain why last month’s recall of 3.8 million child seats didn’t include infant seats, which have the same buckles that can get stuck as the child seats.

Graco Children’s Products Inc. of Atlanta, a division of Newell Rubbermaid, said the child seat buckles get stuck because children drop food or drinks on them. It is sending replacement buckles to owners for free. It said it will also send replacement buckles for infant seats if owners request them.

The February recall covered 11 models of child seats made from 2009 through 2013 by Graco Children’s Products. It’s the fourth-largest child seat recall in U.S. history, according to NHTSA.

The agency 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."

At the time of the child seat recall, NHTSA noted the recall had excluded seven infant car seat models with the same buckles. Both the company and NHTSA have received complaints about stuck buckles on the infant seats, the agency said.

Rear-facing infant seats aren’t being recalled because infants don’t get food or drinks on their seats, Graco spokeswoman Ashley Mowrey said in February. Mowrey had said there have been no reported injuries due to the defect.

NHTSA said Friday that Graco will face fines of $7,000 per day if its response to its request for an explanation of why infant seats weren’t recalled is late or incomplete.

Graco said Friday it will comply with the request for an explanation.