The aim of this project is to produce age-appropriate non-fiction books for children from birth to age 12. These books are richly illustrated with photographs, diagrams, sketches, and original drawings. Wikijunior books are produced by a worldwide community of writers, teachers, students and young people all working together. Text taken from the site.
Another great resource you will want to check out is the Encyclopedia of Life.
The project is a collection of free textbooks and manuals. You can edit any book module right now by clicking on the edit this page link that appears in every Wikibooks module.
The project was opened in response to a request by Wikipedia's Karl Wick for a place to start building open content textbooks such as organic chemistry and physics in order to bring education to humanity and reduce the costs and other limitations to top-quality learning materials. It was started on July 10, 2003 and has been growing steadily since. As a result of the continuous growth, Wikibooks was split into several language-specific subdomains on July 21, 2004. Text taken from the site.
You can see some of the many resources connected to the Wikibooks site. Click here.
BTW, by the way, here is the information about sliced bread from wikipedia.
The phrase "the greatest thing since sliced bread" (and variations thereof) is a commonly used hyperbolic means of praising an invention or development. Sliced bread appears to be something of an arbitrary selection as the benchmark against which later inventions should be judged. It has been said that "the phrase is the ultimate depiction of innovative achievement and American know-how", although it is commonly used in the United Kingdom as well.The popular use of the phrase derives from the fact that Wonder Bread, the first mass-marketer of sliced bread as a product, launched a 1930s ad campaign touting the innovation. Text taken from http://en.wikipedia.org/wiki/Sliced_bread