Google is often the first stop for many kids when searching for information.  two useful alternatives for younger students are

Carrot 2 cluster

http://search.carrot2.org/stable/search

Carrot2 organizes your search results into topics. Presents it as a circle (doesn’t always work) or as a foam tree (see below).  A great alternative to the now non-existent Google Wonder Wheel because it helps students refine search and gain an overall impression of a topic.

Boolify

Boolify is a K-12 audience search tool which helps train people on the use of the Boolean Search Operators “and”, “not” & “or” for standard internet searches. Boolify combines these search operators with a visual jigsaw puzzle approach. By adding and taking away puzzle pieces that represent search words and each of these operators, the students can visually see the effect that they have on the results of a particular web search. http://www.boolify.org/  Simply drag the puzzle pieces to the stage, enter the keywords, and watch as the number of hits goes from millions to thousands to just a few.