6 year-old grandson/video games

I have totally lost the battle of my daughter and her husband letting my grandson play video games almost all the time. My daughter's husband plays almost all day on weekends, and after work. My daughter plays at night. They do not take him anywhere and now it's to another level. They are allowing him to play Xbox where you can talk with the other players. He has found a friend who is five years older than him and my daughter has even admitted that this older boy plays rough and that she is thinking of making my grandson stop playing with this older boy. My question is this. I've not handled this well and my grandson feels guilty that he plays so much. He knows I don't approve and I guess now that he has this friend, grandson has totally changed. Now he doesn't want to come to my house, will hardly look at me, has cried over knowing he shouldn't play games so much, but now that he has this friend he has this defensive attitude and is almost cocky in his behavior. It's really breaking my heart that he will hardly talk to me/look at me. So, how do I handle this? I don't want him to feel guilty, I want him to get out of the house and do things, like we've always done...park, jump houses, etc. I don't feel like I can make him come here...but I can't bear the thought of him just sitting in the house all summer playing games most of the time. How to handle this? When he does come here he just draws pictures and makes up video games. My daughter knows this is a big problem. Not much I can do I guess.