Personally, I view the entire thing as the children's fault. Yes, parents can teach them. Yes, they can stop them from going on the internet, and yes, they can take many precautions and make rules intended to keep children safe. But I remember sneaking out of the house when I was thirteen to go to a rock concert, and finding out that someone got killed there the next morning. I remember waking up at the crack of dawn on certain mornings that I knew my parents where out, and playing video games that were well above my age rating. I remember being grounded for ages, and having the password locked on the computer to connect to the internet. I simply found a keyviewer online, and that was that.
The point is, parents can teach and teach and teach all they bloody well want to. Kids will be kids. Some are smart, some are completely idiotic, and will never change. As for the topic at hand, to anyone other than fetishists of tickling, no one would really suspect tickling to be something that's not acceptable. That's why it is so easy to get a tickling match going on between two women or men that you like, or between you and the person you like. To you, that simple game of "lets see who can hold out the longest" is possibly your secret wish, your fantasy, and you may not change a thing about that game if you and the person you like were just getting in after a romantic evening out. To them, it seems just like harmless fun, the kind of things they would do with brothers and sisters when they were younger.
As we've already addressed, most of these videos are made by two siblings. I know that at the age of 12, if it had been something like, "smack each other with balloons without your shirt on, and see who can make the most red marks with just a balloon" I probably would have done it to prove that I was a man at 12.
Point being, there are stupid kids, and smart kids. But unless they can see things consistently from a completely foreign perspective, they won't know that it's wrong, regardless. And then, even if they do, kids rebel. That's the way, and that will always be the way. In the end, if that's the choice they want to make, that's the choice they will make.
In my opinion, they shouldn't be allowed a webcam at that age though. That's simply asking for trouble.