Generally safe for your computer but it's possible that somebody posting on the site could link to an unsafe website or download. The site has various boards and a few of them have adult material so I wouldn't let kids browse here. Some boards, however, like /c/ or /w/ are usually safe for minors.
Its got some cool stuff, but some HORRIBLE stuff. There is illegal videos of animal and human cruelty, pornography, and viruses in the links. Still, its a neat image board, but I hate the guys that abuse animals on here and should be tracked down.