Parents and parents-to-be got an important lesson in car seat safety Saturday in Brentwood.

Experts say three out of four children's car seats are used incorrectly. They say parents make mistakes like failing to secure the seat tightly enough, leaving harness straps too loose, improperly placing the harness clip or even routing the safety belts through the wrong slots.

To promote safety, the Suffolk County Police Department partnered with Legislator Monica Martinez's office and the nonprofit EAC Network to give parents on-site inspections of their car seats from certified professionals.

"It's really not as easy as taking the car seat out of the box and putting it in your car," said Suffolk Police Det. Lt. Bob Donohue.

While some parents brought their own car seats, others picked up new, free seats for their children at the event. Experts say it's important to get the seat checked by a certified technician before putting a child in it.

Organizers say they plan to hold similar events in the future.