Screen use can have a significant impact on brain development in young children.
A new study looked at 3-to-5-year-olds who used TVs, tablets and smartphones for more than one hour a day.
Researchers said those children had lower levels of development in the brain's white matter.
That's an area key to the development of language, literacy and cognitive skills.
The new study used a special type of MRI.
It is the first study to document screen time and brain structure development in preschool-aged kids.
The study was published Monday in the journal JAMA Pediatrics.