tell them the importance of playing outdoors
the diseases caused by not playing outdoors
getttting fresh air from outside can purify their blood.
make them to watch sports like football, basket ball , cricket etc., so that they will understand that playing together makes them happy
gather all the children of the neighbourhood and conduct a cycling competition . im sure kids do love cycling . so when they ride the cycle once then they will automatically cycle the next day.
hope I helped u..'plz mark as the best!!!