Watch the video first, it clearly lays out the main issues (and yes, he needs to make his bed and clean his room - focus)
In addition to the ones listed there - if your family or your child has an acct, Google is attempting to force convert all pre-existing YT accts to using their real, full, legal name as listed on gmail or G+. It then posts everything that's done on YT onto G+ - if you didn't already have a G+ page, it has autogenerated one for you, without any privacy settings adjusted until you do it yourself. There are ways around this, but it's confusing and complicated.
Also, cannot stress enough the danger of clicking ANY link in a YouTube comment. People are making fake accounts to look like admins and the people who post the videos, then adding comment links that go directly to viruses.
Something else for everyone to consider - a lot of schools use YouTube in the classroom, and may not even be aware of these changes going on. A previously safe demo video of a physics experiment may now have a gigantic ASCII sex scene or a top comment by Barack Obama saying KILL ALL THE JEWS!
I mention that not to be all nanny state, but to ask you to consider, if your 5th grader does see a giant ASCII penis, and a more sheltered classmate goes home to talk to their parents about it, do you think those parents are suing YouTube or your school?Answer Question