I've mentioned SortFix before, but I had an email suggesting that I take another look at it. It's a really simple engine, and one that will appeal to children. Basically it's a multisearch engine that takes content from Google, Bing and Twitter. However, the way in which it works is what is interesting. Simply type in a search (I started with civil war statistics) and SortFix then pulls results from each search engine which it makes available in a tabbed window. It also pops up boxes under the search area called 'Power words', 'Add to search', 'Remove' and 'Dictionary'. These are then populated for you, and you simply click and drag to the appropriate box as needed. This is what it looks like:
Dragging and dropping then changes the search that's being run for you. It's a very simple, but effective concept. Perfect to get children to think about how to construct better searches.