For only $50 for a school, Facts4Me is well worth it. (Only available school hours at that price.  $150 to have anytime access)

Also: uniteforliteracy.com is free and great for emerging readers.

https://wonderopolis.org/

https://www.dkfindout.com/uk/

https://kids.nationalgeographic.com/

https://www.metmuseum.org/art/online-features/metkids/

https://kids.sandiegozoowildlifealliance.org/

https://www.ducksters.com/  (has ads)

Safe Search Kids: This is a custom search engine using Google’s Safe Search features with additional filtering to block more potentially harmful material than if you simply use Google. It is fun, colorful and easy for kids to use.

Google Kid Search: This is another safe search engine powered by Google for Grades K-8. However, please be aware there are ads on this site.

Kiddle.co: Kiddle is a visual search engine for kids, offering safe kids web, image, and video search. Results are vetted by editors.

https://researchitct.org/classicelementary/  free resources from CT State Library

Power Knowledge science  and Discovery Education (both subscription sites, I believe)