Car seats can be deadly places for babies to sleep when being used incorrectly, a new study has found.

When looking at infant deaths in sitting devices, like car seats and strollers, researchers found that more than two-thirds occurred while in car seats. And in those cases, parents were using the car seats as directed less than 10% of the time.

The study, published Monday in the peer-reviewed journal Pediatrics, looked at 11,779 infant sleep-related deaths from 2004 to 2014. While only 3% of those deaths occurred in sitting devices, researchers wanted to better understand what was causing them.

Car seats “aren’t as safe as a crib or bassinet when the child is out of the car and sleeping. … There’s a lack of awareness (about this). I think every parent, including myself, has been guilty of doing this at one time or another,” study author Dr. Jeffrey Colvin told