DocumentaryHeaven is a site filled with hundreds of free online documentaries just waiting to be seen!
I'm sure that practitioners could find the videos on Documentary Heaven by searching the web themselves, but Documentary Heaven makes it easier to find good content.
Through Documentary Heaven users can find documentaries covering all kinds of topics in science, history, politics, business, and many more categories. The videos are sourced from a variety of services not just YouTube.
Note: Documentary Heaven does have some videos in the "lifestyle" category that might not be appropriate for younger learners.