Most nights I read a book in bed to wind down. But when I run out of my library supply, I read articles on my phone instead. I suspect that this digital substitution messes with my sleep. That’s not good for me — but it’s probably worse for the many children who have screens in their rooms at night.

A team of researchers recently combed through the literature looking for associations between mobile devices in the bedroom and poor sleep. Biostatistician Ben Carter of King’s College London and colleagues found that kids between ages 6 and 19 who used screen-based media around bedtime slept worse and were more tired in the day. That’s not surprising: Phones, tablets and laptops make noise and emit blue light that can interfere with the sleep-inducing melatonin.

But things got interesting when the researchers compared kids who didn’t have screens in their bedrooms with kids who did have phones or tablets in their rooms but didn’t use them.

You might think there wouldn’t be a sleep difference between those groups. None of these kids were up all night texting, gaming or swiping, so neither sounds nor blue light were messing with any of the kids’ sleep. Yet Carter and colleagues found a difference: Kids who had screen-based media in their bedroom, but didn’t use it, didn’t sleep as much as kids without the technology. What’s more, the sleep they did get was worse and they were more tired during the day, the researchers reported in the December JAMA Pediatrics.

The results are curious, but raise an intriguing possibility: The distracting presence of the devices may be enough to scuttle sleep.

If a kid is texting with friends before bed and then puts the phone away to go to sleep, he might still be thinking about the conversation, even though the phone is out of sight. To transition to sleep, the body and mind both need time to relax. “You can’t do a 100-meter sprint and then expect to go to sleep. Your body is racing,” Carter says. “Likewise, if your mind is racing, you can’t just expect it to switch off. It’s an organ like all others.”

The research review comes with caveats: Screen time was self-reported, and scientists can’t say definitively whether using electronics before bed (or just having them present) caused poor sleep. It’s possible, for instance, that kids who wake up in the middle of the night are more likely to reach for their phone.

Still, it’s also possible that the mental energy of thinking about a text chain or game — even in the absence of screen-related action — can interfere with sleep. “The use of mobile media devices at bedtime provides socially and physiologically stimulating material at a time when the transition to sleep requires the brain to wind down,” sleep experts Charles Czeisler and Theresa Shanahan of Harvard Medical School write in a related JAMA Pediatrics editorial.

Teachers and health care professionals ought to empower parents to take a hard line on devices in the bedroom, Carter says. Recent guidelines on media use from the American Academy of Pediatrics support that move.

It may be wishful thinking at this point, but if all kids were subjected to an electronics curfew, then maybe they could all get the rest they need. “I think we’re obsessed with our devices,” Carter says. He argues that we should try to keep that obsession away from our children, especially at night.