A helmet, like the one eight-month-old Jaxon is wearing, is the standard therapy for reshaping a baby's flattened skull.
In other babies it's dramatic. It's called plagiocephaly, or flat head syndrome. The number of cases has skyrocketed since the early 1990s.
That's when the American Academy of Pediatrics first recommended putting infants to sleep on their backs to prevent sudden infant death syndrome.
"There's no clear evidence that that has lead to this increase in plagiocephaly, but it's highly suspected," said Dr. Matthew Speltz of Seattle Children's Hospital.
Dr. Speltz is a professor of psychiatry and behavioral medicine at the University of Washington. He led a first of its kind study that compared infants with flat heads to a control group that had normally shaped skulls.
The tests included milestones like the ability to roll over, or crawl.
"We found that our cases were significantly behind the control group participants in cognitive skills or problem skills, early language skills, and especially motor skills," said Dr. Speltz.
He says parents can help babies avoid a flat head. Limit time they spend in car seats and devices that hold them in place. While they're awake, give infants lots of supervised tummy time.
Dr. Speltz says while mild delays might worry parents, they pale in comparison to SIDS.
"Our findings should not at all change the recommendations to put babies to sleep on their backs. That's the safest way for babies to sleep. There's no doubt about that," he said.
The researchers will follow the babies in the study until they are at least 3 years old to see if the learning delays were temporary.
The rate of sudden infant death syndrome has dropped by half since parents started putting their babies to sleep on their backs.