Khan Academy https://www.khanacademy.org/
Khan Academy provides free online video lessons in many subjects, but with a focus on mathematics.
Tinycards https://tinycards.duolingo.com/
Online or as an app, this site lets kids practice various subjects through fun flashcards. Students can select from existing card decks or create their own.
Go Noodle https://www.gonoodle.com/
A classroom favorite, this site offers engaging videos for movement and mindfulness.