Kids' search engines
These are free Web tools, called search engines that both parents and children can use to search the Net for sites that are interesting or entertaining, with the security of knowing that the results of their searches will almost always be appropriate for families. Some kids' search engines rely on filtering schemes to filter out inappropriate Web pages, while others have preselected lists of good content that you can search through.
Kids' search engines sometimes define their content through the use of a filtering tool. In those cases, the results can only be as precise as the tool being used. In other cases, the content comes fom preselected lists, compiled through human review of Web sites, that are highly precise. It is important to remember, though -- kid-safe search engines do not filter Internet content in general, just the results that come up when you enter a search. Search engines alone cannot prevent Web users from visiting inappropriate sites, but they can encourage children to do otherwise.
Whoever maintains the engine often has almost total control over its functioning. Sometimes parents can toggle various settings, but final authority over how the engines work, or over the ways in which Web pages are filtered, is often out of their hands.
Search engines' scalability will vary along with the ways in which they find appropriate Web sites. Those engines which use preselected lists will take time to adapt to the influx of new sites, while those which use an on-the-fly sort of filtering scheme (such as keyword-based filtering or another form of rapid filtering) will usually be able to deal with them without any problem.
Physical safety protections
Kids' search engines can only redirect your children to positive content; they often can't protect your child's emotional or physical well being should they venture away from the sites suggested by the engine.
Even the most expansive search engines cannot comb more than a fraction of all the Internet's resources -- the Internet is simply too big, and is growing too fast. Kids' search engines by definition take a narrower approach to the Internet's content, and as such, they are often less powerful than some of their larger, more fully functional brethren, although they are a good deal more safe for kids.