https://en.wikibooks.org/wiki/Wikijunior
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. The books present factual information that is verifiable. You are invited to join in and write, edit, and rewrite each book and chapter to improve its content. Our books are distributed free of charge under the terms of the Creative Commons Attribution-ShareAlike License.