David Mooney has seen the injuries too many times: children with broken backs or torn intestines caused by seat belts.
"They call it 'seat belt syndrome,' " the Boston pediatric trauma surgeon said. "It's a classic injury for kids in accidents who have been restrained in cars without booster seats."
Now, Mooney hopes he'll see a decline in business, thanks to a law signed by Governor Deval Patrick last week that requires children to be in car seats or booster seats until they turn 8 years old, or reach 4 foot 9 in height.
"Sure it's inconvenient and nobody likes to be told what to do," Mooney said. "But our convenience doesn't outweigh the safety of our kids."
Sharon Johnson, a South Boston mother who had a close call with her son, called the new rule "a fabulous idea."
"It can save so many lives," she said, while shopping at the South Bay Shopping Center with her son, Connor.
Two years ago, the account executive was on her way home with Connor when a driver ran a red light and crashed into her, totaling her car. Though Connor, now 4, suffered whiplash, his car seat pre vented more serious injuries. Now, Johnson said her son rides in a car seat even on planes. Johnson purchased a car seat that converts into a booster seat, even though it was more expensive.
"You feel safer because you can't control how other people drive," she said. "It's so scary."
Seat belts are designed to ride across the tops of the passenger's hips and shoulders, but on children and smaller adults, the seatbelt cuts across the abdomen instead, which can cause serious injuries in an accident. A booster seat, which sells for as little as $20, raises the child's body so that the seatbelt hits the right spots, reducing the risk of injury.
Thirty-eight states have booster seat laws, up from four just seven years ago. Massachusetts' new rule, which carries a $25 fine, will go into effect in mid-July.
"It's good because you still see parents without anything for their kids or babies riding in the front seat," said Taheera Massey, a Dorchester mother.
Though her 8-year-old just stopped riding in a booster seat, Massey said she kept it for longer trips because there's a greater chance of being involved in a serious accident on the highway.
But she said her 5-year old is already clamoring to get out of his booster.
"He says 'I'm a big boy,' " she said. "I tell him, 'You've got three more years.' "
Geoffrey Green of Brookline said if nothing else, the law emphasizes the importance of booster seats. Though he uses one for his 7-year-old son, not all of his friends use them for their children.
"It makes it easier for me to insist," Green said in a telephone interview. "I'm not just that safety-conscious nut."
Two months ago, Green's wife was hit head-on by a 97-year-old driver. Though his children weren't in the car, Green said the experience made him even more safety conscious.
"It just made me realize it can happen at any time," he said. "You can't plan for that."
While the new rules emphasize safety, not everyone appreciates being told what to do by the government.
"I see it as an intrusion of my rights as a parent," said Stephen Breen, a North Reading stay-at-home father.
Though Breen cares about the safety of his four children, he said in a phone interview that the government should not tell him how to raise them.
"I don't need the law to tell me at what age, at what maturity level, at what height, my kids need to be in a booster seat," he said. "I'm frustrated they're getting involved when there are other, more important issues for them to deal with."
To Laura Finnerty, the new law is just another step in Massachusetts becoming what she called, "a nanny state."
"They tell us what we can eat, where we can smoke," she said.
At 4-feet, 11-inches, the 37-year-old Bedford resident wondered if the government would soon force her into a booster seat.
"What are they going to think of next?" she said.
Green, however, said that like motorcycle helmet laws, the new rules shouldn't be taken as an infringement on civil liberties.
"People don't realize that the costs are not only on ourselves, but society in general," he said.
Tania deLuzuriaga can be reached at email@example.com. Globe correspondent Michael Naughton contributed to this report.