My kids’ hobby

I don’t know what to do with my kids’ hobby. I am talking about the free games they are playing all day long. Before these free games appeared, my children use to have a normal life. They used to play football, tennis and to have a lot of outdoor activities. Now, they don’t do anything else but sit and play these games. Sometimes they also fight over the games. Can somebody tell me what could I do to help my children?