This is an extremely awesome website that I should go to more... but the reason why I say "more" is because there's buttloads of adult content. If you want an example of this, try Derpcraft.
Luckily, they have their own rating system that tells you which games/movies/works of art are suitable for children. For example, E can be played by a 5 year old and they can still be allowed. T is recommended only if you're 13+. M is for people that grow up too fast, and A is the same as M, except it's only for 18+ no matter what.
I'm 10 years old, so I personally prefer things like Where's Derpy, Windows Doors, or even Interactive Buddy.
They even have a spam filter so that you don't see myfunonlinegames.com absolutely everywhere you go!
This is overall one of my favorites, and has been since I was 5 years old. (I didn't understand inappropriate stuff back then, so I was banned by my parents when I turned 6. Then I was banned from Wikia when I was 9 years old, but I got Newgrounds back, so overall 2-4 years this has been one of my faves.)
Great website serving as the largest flash portal of the past 2 decades. Flash videos and .mp4 videos are to be uploaded as well as audio and art. The forums may possibly discuss topics that contain adult content, but the rules indicate a warning must be given beforehand, so that viewers may never unknowingly be exposed to things they aren't aware of. Many games and movies are themed for children, whereas still thousands of others are themed for adults of all ages.
This site is the best free content portal that I have found for now containing a lot of different stuff: it contains music, art, sounds, animations and games. About the kid safety: listen, it is not a problem for kids, is a problem for THEIR PARENTS, that should care about what do they children watch in Internet.