Ds1 (9) not allowed on YouTube unsupervised. This is because I am concerned about him scrolling through comments and clicking on related videos that turn out to be anything but. Have explained this to him, as has dh.
The other day I left him in the middle of watching a Minecraft video (it was really long and I had better things to do, frankly, like looking after two other children) with the instruction that if it finished while I was out of the room he needed to turn it off and go and do something else. Came upstairs to find him 5 minutes into another video. Told him off for abusing trust and he wasn't allowed on computer again for a couple of days.
This morning he asked whether he could go on the iPad. Said yes because I thought he was playing on Garage Band, which is all he ever uses it for. Then came in and realised he was watching Lego Minecraft stuff on YouTube - I didn't even realise he knew how to get on to it by himself 
. I took it off him and sent him to his room, and he wouldn't go. Had to take him by the arm and physically put him in his room and told him to stay there, two minutes later he came out saying he was going to get something to eat - bearing in mind he had just had his breakfast, he was clearly just flexing his muscles.
He's back in there now but I am fuming. Part of me wonders whether I am being overprotective, because plenty of people allow their kids on YouTube, but it's more the issue that I have set a boundary and he is refusing to stick to it, so I can't trust him. I'm beating myself up now though about whether I have been too heavy handed. AIBU?