I had my grand-nephews visit me when they were 7 and 9 yrs. old. They had trouble putting down their little game toy, even when they were at the dinner table. From what I understand, they both have Facebook accounts. I don't belong to facebook, twitter or my space, and don't intend to ever join.
It seems that the kids (and sometimes their parents) don't even live 'normal' lives anymore. They post what they had for breakfast, take selfies of themselves at the shopping mall, and can't do anything really without relating to posting it on Facebook, and maybe outdoing the last person. Those social sites seem to be very competitive, and very hurtful by those who like to bully.
I don't have kids, but I would definitely limit their computer/video-game time if I did. The egg throwing thing would have been less ridiculous, if they just sat around talking to each other in person, and decided to do it for fun. The fact that they were copying someone who did it on facebook makes it creepy, IMO.