When children are involved in a car accident, they are less likely to be injured if grandma or grandpa are driving rather than mom or dad.
The study, published in the journal Paediatrics, looked at five years' worth of data on U.S car crashes involving children younger than 16.
It found that when grandparents were at the wheel, 0.7% of children were injured in the crash. That compared with 1% when parents were driving.
When the researchers considered other factors - such as the circumstances and severity of the crash - kids riding with grandparents were half as likely to be injured, versus those riding with their parents.
"That was absolutely unexpected," said Dr. Fred M. Henretig, an emergency medicine physician at the Children's Hospital of Philadelphia and the lead researcher on the study.
And in fact, grandparents were less likely than parents to follow experts' latest recommendations on strapping children in
- like having kids younger than 13 ride in the backseat, and using booster seats for children who have outgrown car seats but are not yet tall enough to properly use adult seatbelts
"For so many grandparents, it's been 25 or 30 years since they've been driving with young children, and a lot has changed since then," he said in an interview. "So they may be a little out-of-date."
So why would children riding with grandparents have a lower injury risk?
That's not clear from the study. But Henretig speculated that there are "subtle differences" in parents' and grandparents' driving habits that affect crash-injury odds - as overall, there were no major differences in the type and severity of their car accidents.
"Maybe grandparents were going a little more slowly, or not following the car in front of them quite as closely," Henretig said.
He also speculated that when grandparents are taking kids on the road, it is something of a special occasion, and they may be completely focused on keeping their "precious cargo" safe
. They may also be less distracted than busy working parents tend to be.
"They may be more likely to keep both hands on the wheel, eyes straight ahead - not using their cell phone, or fiddling with the radio, or thinking about that last email at work," Henretig said.
The findings are based on data from nearly 12,000 children from 15 U.S. states who were involved in car accidents between 2003 and 2007. Almost 10% were riding with a grandparent at the time, but they accounted for less than 7% of all injuries.
Like parents, grandparents almost always had children strapped in. But grandparents were less likely to conform to experts' latest recommendations: they were out-of-step 25% of the time, versus 19% of the time for parents.
"So there is definitely room for improvement there," Henretig said.
He suggested that parents help by making sure grandma and grandpa know how to properly strap their children in, showing them how to use car seats and booster seats if needed.
This study looked only at children's injury risk during a crash. Henretig said he is not aware of any studies examining whether grandparents are less likely to have an accident with their grandchildren in the car, compared with parents.
In general, he noted, people in their 60s and beyond are at greater risk of having an accident than younger adults. But it's not clear whether grandparents driving young children have a lower risk than other seniors.
Do you think your kids are safer with you driving than with their grandparents?