Children’s eyes are anatomically slightly different, and they do let in more light, and a new study suggests that exposure to bright light before bedtime can throw their body clocks out of whack, reports the New York Times.

In an article published this week in the journal Physiological Reports, researchers report on an experiment in which they measured levels of melatonin, the hormone that regulates sleep, in a group of 10 children, ages 3 to 5. First they had the children follow a regular sleep schedule for five days, and checked their saliva several times a day to measure their baseline levels of melatonin.

Then, on day six, they turned children’s homes into low-light “caves,” covering the windows with black plastic and swapping in low-wattage light bulbs. Lameese D. Akacem, an instructor at the University of Colorado, Boulder, who was the lead author on the study, said that the children spent the whole day in the dim light, again with researchers tracking their melatonin levels.