How about standing desks at home ?
In Hong Kong, the Advisory Group on Health Effects of Use of Internet and Electronic Screen Products convened by the Department of Health released a report in 2014 with recommendations on limiting "screen time" and advocating "going outdoors and being physical active" for children and adolescents. In addition to efforts of the Government and community sectors, role of parents and carers are equally significant in overcoming childhood obesity. They should stay alert to their children's diets and ample opportunities for children to exercise.
So, parents can just urge them to exercise? stop them from playing video games? It might not work well. However, change their desk to height adjustable desk might help a bit. To help reduce the screen time and increase exercise time, we can't just force them, we can make a minor change on their desk.
It is very simple, when they play video games or watch series, by using standing desk, they can easily adjust the height by one button, they can switch their seated or standing posture freely, to stay physical active even when they are with their devices. This is the easiest way. Of course, they should not spend too much time on computers or phones, they still need to walk around or go outdoors for sunshine!