A group of researchers in New Zealand studied the pre-sleep activities of more than 2,000 children and teens ages 5-18. They found that the kids averaged 30 of the 90 minutes before falling asleep in front of a screen. Most of this was spent watching television as opposed to using a computer or playing video games.
Interestingly, the researchers found that those children who fell asleep later spent more time watching TV. This may be because of the content, or the increased light exposure. Regardless or the cause, it is consistent with what other researchers have found, and suggests that limiting screen time (or eliminating it altogether) may be an effective strategy for helping children and adolescents get an appropriate amount of sleep. This is important, as we know that insufficient sleep adversely affects cognition and behavior, as well as physical and emotional wellbeing.