I work as a nanny with children in the grammar/primary school age range and this website is fantastic for homework and just "general fact finding". Schools in my area in Australia also use wackysafe.com, which tends to be provide better answers to questions asked by pupils.
We use KidzSearch in our school and love it. The search results are safe and provide quality academic content for student research. There are other alternative services, but our students like KidzSearch the best. They also have an extensive collection of really good free educational games that we use for teaching.