PicBlock is an excellent application that helps you block undesired websites and pictures so that your kids cannot have access to them.
The program is fully customizable and allows you to state exactly what you wish to block. You can set the sensibility level (mild, normal or strict), set notification types for blocked content, customize the unblock keyboard shortcut or set passwords to unblocked content, set a keyword analysis, among other things. You can also set passwords for viewing logs, accessing settings, disable the program, etc. and even run the program in silent mode, setting a shortcut key to launch its settings. The program also includes a log that registers all blocked and unblocked content, so you can see what sites your kids have tried to access or accessed. You can even add or import a list of key words that will make the program block the sites that contain them, enter a list of URLs that you wish to block, and sites that you wish to have access to without problems.
In short, PicBlock is a useful program that will help you protect your kids from harmful content and it can also be used for other uses, like preventing your employees to access certain sites that will keep them away from their working duties.