National Geographic Kids: Games, articles, and videos about animals and nature
Hour of Code: Learn coding skills
Khan Academy: Free online video lessons in math and other subjects
Refreshers for parents on algebra and geometry
Scratch: With Scratch, you can program your own interactive stories, games, and animations — and share your creations with others in the online community. Scratch is a project of the Lifelong Kindergarten Group at the MIT Media Lab.
Lessons about coral reefs, mangroves, etc., via Reef Relief
Mystery Science: fun, easy science lessons for grades K-5 (sign up for free access for one year)
60+ fun and easy science experiments for families, using household ingredients
Quarantime – Online school with Science Mom and Math Dad. Each show will feature a science lesson, math activities, interactive games, and stories. Aimed at kids age 7-12.