The Guardian, as one of the largest UK newspapers, is sure to have a very safe and secure site, full of knowledgeable information. Indeed, it is safe and secure. I use it frequently to check the university league tables and for film reviews, as well as just general news. However, do be careful of any sidebar ads, but that can be said for pretty much any website!
If you know your way round YouTube, odds are you've probably heard of RayWilliamJohnson, #1 most subscribed channel on YT and presenter of the webshow 'Equals Three' or '=3'. He's now moved to greener pastures, setting up a new website to post his blogs, music videos (under his alter ego band name, YourFavouriteMartian) and other little delights he has found in his travels around the interwebs.
For safety, this is rated high. For ads, I recommend the Adblock Plus for Mozilla Firefox to stop any annoying ads which could cause annoyance through a slip of the finger.
While the site is reatively safe, this is definitely going under the red rating for harming YOU, and those watching. I mean, a prank? You've gotta have guts, or misplaced stubborness to WANT to see this. Because it'll take a lot to get rid of it once it's been seen!
Most definitely not for children; if they do somehow click this, and you see them doing it, get them away from it IMMEDIATELY.
This site is rated safe, bar a few ads (much like WikiAnswers) but they can be easily avoided.
However, if you are going to pose a question here, as with WikiAnswers, be careful. Ask a stupid question, and stupid answers will be ready to rebound and bite you on the bum! There are a few trolls on here, but if you keep stupid questions (such as the classic gem, 'Did my dog get me pregnant?') out of the equation, it is smooth, troll-free sailing. Otherwise, you might find yourself on Unfriendable.com or Memebase!
Post a question, and the community of people will be more than happy to lend you a hand with your dilemma. It even may include Wikipedia snippets if your problem fits the bill. The site is safe bar a few ads at the bottom of the page, but it is easily avoided.