I walked into a colleague's house recently and was struck by what I witnessed. Five kids ranging from about 5 to 13 years all perched on the couch immersed in their tablets and smartphones with headsets. I told my colleague that 20 years ago she would be struggling to find these kids because they would be outside all day playing rough with their friends. Not today. Today kids spend half as long playing outside as they do looking at their screens.
Without enough physical activity, kids' physical development is stunted. And their imaginative and creative potentials may not be fully realized. Even more importantly, unsupervised, these kids learn a lot of garbage online. No, "parental control" is for amateurs, even the kids would tell you. Only realistic solution is to physically make them to go outside and play. And restrict their access to the devices.
It's important that kids between ages 5 and 15 years engage in physical outdoor activities. They won't all be Lebron James, Serena Williams or David Beckham. If you don't want them playing American football, there is soccer(no it's not a communist conspiracy, ha!). Anything to get the kids interested in sports and playing outside. Otherwise you would raising a generation of weak "screen zombies!"