A new report sheds light on the importance of dark when it comes to kids' sleep.
It found exposing preschoolers to an hour of bright light before bed drastically reduced their production of melatonin, the hormone that regulates sleep. Those levels stayed low for almost an hour after lights out.
Researchers say structural differences in the eyes of children may make them more vulnerable to light.
The take away for parents? Dim the lights and take away any electronics before bedtime.