Watches too much YouTube
Before You Begin
Pause and breathe. Even if this shouldn't be happening... accept that it is and embrace it with composure and calmness.
Calmness is the only way forward because without calm, there is no possibility for receptiveness and connection. Your child won't give to you any more than they see from you.
Never forget that a strong connection is fundamental, as there will be no correction in them if there is no connection with you.
The Core Problem
Watching YouTube has become so habitual, the child is blind to the passive harm it is doing to them.
What Will Make It Worse
Abruptly taking away their access to YouTube will escalate the conflict between you and the child, not address the core problem, and not teach them anything that they could apply to similar situations in the future.
What The Child Needs
1. To understand all of the good things that YouTube is displacing in their life: Share a list of all the fun and positive things that the child has stopped doing, as well as the bad things that have sprouted up as a direct result of them spending so much time on YouTube. (For example, they could now be less motivated to think for themselves, be creative, have new experiences, get exercise through outdoor activities, or act in a way that is true to them vs. imitating what they are seeing in the videos.) Additionally, point out any emotional consequences you are seeing, such as a consistent drop in their baseline happiness and rise in their irritability. Help them see that hours of YouTube isn't good for them.
2. To go back to what they loved: Remind them that before they got so attached to watching YouTube, there were tons of things they enjoyed. Help them make commitments to do those things again, or pick a new activity or sport that they can get excited about and dive into.
3. More time making memories with you: Kids of all ages want to go on adventures, have laughs, try new things and generally make happy memories with their parents. Your child will be more likely to turn away from YouTube and towards you if they see that opportunity. Make it a point to do more things with the child that outshine the draw of YouTube.
How To Have The Conversation With Your Child
Find a time when you know the child will be open to talking with you.
Start with an example the child would completely go along with. For instance, state that candy is fine once in a while but that if you replaced all their meals with candy it would create problems and they would be worse off for it. Next draw the comparison to YouTube, and share you are seeing problems as a result of their excessive viewing.
Express understanding that while YouTube seems harmless, just like a single piece of candy, it has gotten to the point where they are watching the equivalent of a mountain of candy.
In a caring tone, explain what they aren't seeing for themselves, and begin to talk through point 1 above ("What The Child Needs").
Then move on to the solution of points 2 and 3, with the promise that it won't take long before they realize what they have been missing out on, and are grateful that they broke away from habitually watching YouTube.