Youtube isn't a monolith, it's a medium--rating it as a single site is more like attempting to rate "cable television" than any particular show, or even channel. You wouldn't let your kid watch random TV without supervision, or surf the 'Net randomly on their own, so don't do the same with YouTube. Simple.
With appropriate supervision and screening (we usually check videos out in advance and put them on our "favorites" list before letting our son pick, unless they're from a reputable kid-friendly account--working from a personal account interface minimizes exposure to inappropriate comments and "related" videos), YouTube can open up a world of art, music, and performance experiences that most people, kids or otherwise, wouldn't have had access to even ten years ago. Drum-crazy preschooler want to know about Javanese gamelan music? There's video. Daughter nuts for polar bears? There's National Geographic footage. Reading "Just So" stories in school? Check out the gorgeous Russian animated versions from the 80s--you won't find those on Netflix! Can't remember all the lyrics to that song your son learned in Kindermusic? It's probably been posted by a cheerful teacher with a happy kid chorus and a bouncing ball highlighting the words across the bottom of the window. Haven't gotten to visit Grandma for a while? Mail her an inexpensive webcam, a copy of your kid's favorite bedtime story, and instructions for uploading the footage (and disabling comments from strangers) in time for the young'n's birthday. The possibilities are endless.
I'd take our carefully-selected YouTube experience over 90 percent of the commercialized junk on Nickelodeon or the Disney Channel any day.
This title contains:
Violence & scariness
Drinking, drugs & smoking