Writing an essay

It is true that a lot of young people choose playing videogames in their free time. I believe that some limitations are necessary to avoid that it becomes an addiction. ("...avoid it becoming an addiction." is a more common construction. But what you wrote is fine.  I am guessing you have learned "british" english...eh?).

Firstly, children who spend their free time playing videogames, frequently they get bad grades at school. That is because they dedicate more time playing than studying and doing homework. I believe that they have to be controled by parents and agree when is the time to for playing and studying.

Secondly, playing videogames contributes to having a poor social life and get overside (I don't know what you mean by overside) because it involves staying being alone and static activity.

On the other hand, I believe that all the children should practice some sport instead of playing videogames. So, if they dedicate time to doing sports they would improve their healthy and their social life by meetting people, in a team sport for instance.

To sum up, in my view, parents should offer to their children to do a sport and control and limit the time that they dedicate playing videogames.

Very good writing.  This seems too easy for you..I think you need to work on harder constructions...maybe writing about the past?  saludos -Sven