Parents hoping to help their children get a better night's sleep may want to have the children leave their cell phones on the breakfast table overnight.

The problems associated with poor sleep are diverse and well documented, and they can set the stage for negative health consequences that may last a lifetime.

More immediately, too little sleep contributes to poor academic performance, behavior issues, as well as childhood and adolescent obesity, and high blood pressure.

Small screens, which include Internet access and gaming, are more interactive and therefore more arousing. They can also be the source of alerting sounds for calls and texts that awaken the children’s sleep rhythms and disturb their sleep cycles.

Researchers collected data from over two thousand fourth and seventh graders in an effort to better understand the connection between screens in the bedroom at night and the quality and duration of the children’s sleep.

They asked the children in the study about their weekday bedtimes and wake times, and about the presence of TVs and small screens (cell phones, smart phones, iPod touch devices, etc.) in their bedrooms.

Fifty-four percent of the students reported that they slept near a small screen, while 75% had a TV in the bedroom. Not surprisingly, there were more seventh-graders (65%) with small screens than fourth graders (46%). Seventh graders slept for an average of 8.8 hours per night while fourth graders slept 9.8 hours.

The data revealed that both TVs and small screens caused sleep loss, but small screens were the culprits when it came to excessive daytime sleepiness.

The children who slept near small screens reported 20.6 fewer minutes of sleep per weeknight than those who did not sleep near small screens. Those with a TV in their bedrooms reported 18.0 fewer minutes of weekday sleep.

When the students had either small screens or TVs in their bedroom, they went to sleep about 30 minutes later than their peers. Only the children who slept near a small screen were more likely to report feeling tired during the day.

There are several reasons why small screens may cause both less sleep time and increase the likelihood of daytime fatigue, the researchers say. Receiving phone calls and text messages around sleep time can be inappropriately stimulating at bedtime.

The use of screens at night may displace sleep time by delaying bedtime and leading to shorter sleep duration. Watching exciting or disturbing content on screens may affect sleep onset and quality.

One reason why phones seemed to produce more daytime fatigue than television, according to the researchers, is that TV watching is a passive activity, while small screens, which include Internet access and gaming, are more interactive and may therefore be more arousing.

Cell phones can also be the source of alerting sounds for calls and texts that awaken the children’s sleep rhythms and disturb their sleep cycles. The child may then have difficulty falling back to sleep.

Screen light that is bright and short-wavelength may change circadian rhythms and impact release of melatonin, the "sleep hormone." Additionally, because small screens are held closer one’s face, they may have an enhanced impact on biological sleep/wake cycles.

Most parents already know that watching TV or using small screen devices, instead of going to sleep, interferes with a child’s restful sleep, but this study makes it even clearer the sorts of problems that bedtime screen time causes.

What parents may not appreciate is the extent to which disturbed sleep impacts their children’s immediate and long-term physical, social, and emotional health, as well as daily productivity.

Screens are pervasive in our lives and setting limits is not an easy task. However, the goal of preventing both short- and long-term health problems in children makes it necessary to rise to the challenge.

Help your children become aware of the effects of screen time at bedtime and have them leave their phones out of their rooms at some agreed-upon hour. Parents may want to set an example, especially since cell phones are bad for parents' productivity too.

The American Academy of Pediatrics offers both some excellent tips for parents on setting limits for media use, and a media time pledge that all family members can make.

The study is published in Pediatrics.