WebFilter is a free Chrome extension designed to block access to objectionable or dangerous sites, including those that are pornographic, harbor malware, show drug use, or are heavy bandwidth users. It's a generally useful tool, although it is somewhat marred by its surprising inability to block at least one very obvious problematic site.
Setup is simple; simply download the extension with Chrome. At that point, WebFilter stops Chrome from visiting the dangerous or problematic sites. When you (or more likely, one of your children onto whose browser you installed the extension) try to visit one, you can't get there, and get a page that reads "Web Access Blocked: The following web Access is blocked by Cloudacl," followed by the URL of the site.
That's all well and good. But it won't block access to every objectionable site. For example, it didn't block access to sex.com, a surprising oversight. However, you can always add sites you come across to a blocked list. Still, if you're trying to protect a child, this won't help at all, because the child will have already come across the site, and isn't likely to block him- or herself from future visits.
WebFilter is customizable, so that you can decide which types of sites to block. For example, block sites related to pornography, but allow social-networking sites and sites that suck up bandwidth.
Even there, though, there are some problems with the program. Inexplicably, one category lumps abused drugs and marijuana in with abortion. What drugs have to do with abortion isn't at all clear, and some parents may well want their children to know about abortion, even if they don't want them visiting sites related to drugs.
The final problem with WebFilter is that it simply won't work for older kids. There's no password mechanism for turning it on and off. So if you have a child who knows his or her way around a computer, they'll be able to bypass it by simply turning it off.
WebFilter is free, and so may well be worth a try depending on what you plan to use it for. It's most suitable if you want to block your own access to certain sites, or if you want to block younger children visiting problematic sites. Otherwise, you likely won't want it.