I believe the book “Remotely controlled” which Bluebell Finn mentioned is by Aric Sigman. He has done a lot of research into the effects of screen time on brain development. I went to a talk by him, and since then we have limited T’s screen time, because I felt the information presented at the talk was very compelling.
My OH spends absolutely ages in front of the computer, so not a good role model for T, and I’m not entirely innocent myself of course! So if T wants more time than I feel is “safe”, I tell him that it can be harmful. As others have said, it does vary a lot. He may have a few weeks where he is into a game on the Lego site and wants to play it every day, then have other times when he forgets about it. We don’t have tv, but we have a computer and screen that we watch dvds and downloaded things on, again that varies.
There is one of those smart boards in T’s classroom (4 - 9 yr olds) and they often watch films and cartoons at school, which I think is unnecessary. I hate the fact that he is watching a screen when it isn’t even anything he would have chosen to watch.
