LYNN – A parade of cars and trucks stopped by the Lynnfield Street firehouse Tuesday where firefighters and police officers conducted free child-seat safety checks.The event was part of a series of checkups across the state to mark the first ever Massachusetts Child Safety Seat Day. Nearly 30 drivers took advantage of the inspection in three hours, mostly women – mothers or guardians – with one or two car seats strapped to the interior.”A lot of the people want their kids to be safe, but they don’t know how to correctly strap the child seat or booster seat into place,” said Lynn Fire Lt. Joseph Zukas. “In most cars made after 2003, there are latches connected to the floor that make it easy to buckle and unbuckle the seats.”Zukas said many parents were unaware that the chest strap must be customized for the age and size of the child. “Strap it across the child too high up and you could strangle them. Too low and the baby can come flying out,” he said, adding that car seats over six years old are considered defunct. “It’s like an expiration date. At that point, the seat should be replaced.”Laurie Spencer of Lynn had the state-certified installers check the security of the car seats in her Volvo station wagon. “I have a 1-year-old, Amelia, and a 4-year-old, Madison, who is in a booster seat,” said Spencer. “I’m glad I stopped by because I had no idea about the latches built into the car where the seats can be attached.”Jen Banville of Lynn found that the two car seats in her Ford Expedition were too loosely strapped. Sylvia Marroquin of Lynn had a similar experience and was grateful to ensure that her children, Valerie, 3, and Emily, 4, will be safer for it.Fire Chief James Carritte said the car seat inspections will continue as a public service. “We’re getting more people certified and that’s great,” he said. “We want to have it so that there are always two installers available.”Firefighters from Lynn, Peabody, Lynnfield and Danvers assisted at the inspection site Tuesday, as did a Gloucester police officer.Zukas said a couple families with aging or malfunctioning car seats were given new ones as a courtesy. “We had a few here that were donated, so those people definitely left here more safely than they came in,” he said.Inspections were also held Tuesday in Brighton, Lowell, Springfield and Worcester.Child passenger safety equipment grants were awarded statewide to 33 communities and non-profit organizations to help implement the new booster seat requirement of the Massachusetts Child Passenger Safety Law, which goes into effect July 10.