After a summer of chatting and texting, it may be hard to get your kids to cut back on their cellphone usage. However, insisting that phones be left in a particular spot before bedtime—such as in the kitchen, or by the front door—may improve your child's sleep. A study of 1,656 schoolchildren between the ages of 13 and 16 revealed that 62 percent of them use their cellphones after they've gone to bed. The researchers followed the kids for a year and found that those who used their cellphones after bedtime less than once a week doubled the chance they would feel tired the next day.