This kids' online encyclopedia includes maps, videos, images, a read-to-you function, links to Spanish language articles, citations. Each article has a link to a more in-depth article in World Book Student.
National Geographic Kids includes all magazines from 2009 to the present, as well as books, videos, and images. It's a good source for images, videos or fun facts, which may take some digging.
This resource does not provide leveled text or read-to-you.
Extremely cool 3D visualizations of asteroids, the solar system, the 2020 Mars landing. Some other visualizations on this page require an app. Be sure to click on the ⓘ or "Learn" links to get good information.