WeeWorld like all other social networking websites has it's pros and cons. I don't believe it's a site for kids though. For one, most younger teens that are 13 tend to be immature and inappropriate. There are even 10, 11, and 12 year old sneaking onto the website by lying about their age. You can do this same thing on any other sites like facebook, twitter, myspace, and etc.
I've read some reviews people have left about this site and not all are completely true. I myself have an account on WeeWorld and I'm 15. There are, probably to your surprise, a lot of good people on this site. I mean WeeWorld does have it's dark side with inappropriate people that speak of sex, violence, drugs & alcohol. If you want your child or teen to stay safe at all times, then show them what it is to be a responsible user of the internet.
Meaning staying away from giving out any kind of personal information, not dating online, lying about their age, being inappropriate (cybering), and so on. Honestly, all social networking sites can be just as bad as WeeWorld at times. No site is perfect and there are always going to be those people that you absolutely never want to come into contact with.
If you decide you want to allow your kid to join, that's fine. If your child is being bullied or harassed your child can simply block that person and report the issue to WeeWorld.
Overall, WeeWorld isn't that bad of a site. I enjoy it during my free time and catch up with some really cool people I've already met on there (most of which are my age or older).
On another note, there are adults on this website. This site I believe was originally intended for adults 18 and up. But they lowered the age to 13 and up. But the adults will likely state they are adults and not lie. But of course there will always be the dangers and chances of your child coming across an adult lying about being a teen. Just stay safe and be safe, that's all you can really do. :)