The site can be good or bad, it just depends on the vid you watch.
I see no real problem with the site except for the fact that in the comments, people will often insult the creator of the video, and/or the video while using crude language etc.
But it's simple to keep YouTube a safe environment. All you have to do is know what you are searching for. Take me for example, I usually search for the user-made music videos of my favorite movies such as Pirates of the Caribbean, or Spirit: Stallion of the Cimarron.
I still agree, that you should watch your kid, because sometimes people will tag a video about something crude with words like 'Pirates of the Caribbean', because they know it's a popular genre, and want more people to watch their video.
Overall, it's a great site if you know what you're doing!
(Btw, if you need any assistance, you can messege me on my account there.