I think it's pretty fun on Kongregate. Most users are nice and will be curteous, but some like to be mean and say curse words and that kind of stuff. But that's mostly just in chat or forum. Though there are some bad games on there, Kongregate's mostly clean. I'd say...anybody under 11 can play most games on Kongregate. Anyone 9 or under will need supervision to avoid exposure to bad stuff on there. The user content is great, too, but mainly the bad stuff on Kong is the mean/heavily cussing users. Most people on Kong are very clean and may only curse occasionally. Some people, however, tend to curse and talk stuff unsuitable for most people under 13-14.
This site is good, for older kids. The profile slant can be definitely addicting, as certain achievements garner "badges". The all consuming hunt for badges is what drives most of the gamers on the site. Also, the chat feature can reveal some good or reasonable character, but it also can lead to kids jauntily sidestepping the profanity filter with the use of periods, spaces, misspellings and dashes.
A few games on the site are actually educational, like Globetrotter XL, a geography game that is actually fun, and Notecatcher, which teaches classical music with beats. But some games are violent, featuring zombie shooting, and some use of magic in the role-playing games. However, political games that jab at politicians, and sexually oriented games are never uploaded. The gamers on the site are encouraged to review games, and the uploader/developer will get points for how his game does, which prevents games that are not from being uploaded.
Overall? Just be careful about when they get on unless they are at least fourteen. This is the YouTube of flash games, and like YouTube, it can get iffy at times or places. Watch the forums, as well.
There are so much positive and negative contents on Kongregate, the way you should use the contents is to dodge the Negative things, simple, and the users below 13 years old should be watched by their parents and it's should be okay if they're behave properly on messages, game comments, reviews and forums.
By far the best site for free online gaming i've come across in the many years of playing i've had. Some occasional bad chatrooms, but can easily be turned off or switched. By playing the user uploaded games you earn badges and points by accomplishing certain achievements. Some really great games which can help make a boring evening at home a very enjoyable experience.
Many of the other reviews comment correctly and accurately on a variety of Kongegrate features. The details of the inappropriate content within the chat rooms and forums, however, are not complete enough. It is not merely "salty" language, but an extremely high amount of sexual vulgarity and verbal pornography. These conversations are dominated by young males and include casual treatment of violent sexual behavior with rampant sexual propositioning and mistreatment of women. The reporting features do not work or are completely ignored and the "moderators" are frequently active participants in the behavior or turn a blind eye to it, even when asked to do something about it.
I am a parent and I played the site for over a year before I finally got fed up with these occurrences and the complete lack of concern that Kongregate has regarding these problems.