a good choice for the curious kid (or kid at heart)
Although some content is technical, knowledge-hungry kids will find this site worth the read. Ads are present, but are kid friendly and by far the least interesting part of the web page.
Also, i like this site for children because it encourages reading for personal pleasure and imaginativeness/curiosity: two things that are not always easy to instill in some children.
Also, the content is aimed at all age groups, kids to seniors. Because of this, the language (minus technical terms) is easy to read and understand, and adults can find interesting topics, too.
From, "how bed bugs work" to, "how credit scores work," any curious, literate person can enjoy howstuffworks.com.