Video game

I like video game, but I do not support that it is good for kids because I have an example of my cousin.
He is ten years old, he spends a lot of time with his video game. He becomes overweight, his eyes are having problem and wearing glasses, sometime he really aggressive. Actually, he is an intelligence boy, but he does not do well in his study because all the time in school with his classmates, he just talks about the video game. His name on the board everyday. His teacher talked to my uncle about this, and my uncle asks him to study hard and try to teach him when he has time.
I was remembered, there was a new video game came out, and he asked my uncle to buy for him, but my uncle refused. You know, what did he said? He said " I will get number one in class if you buy this game for me". My uncle agreed and finally he got number one in class. So my uncle kept his promise. After he got it, his study came back to the same level as before. He did like this so many times so I asked my uncle is it a good idea that all the time we want him to study hard, we need to exchange something that he want? (What do you think in this case? Please give me some ideas).
As I read the article about kid effect from video game more than get advantage I'm really not happy about that I don't know what is going to happen with my cousin's life. He just like my brother.