Summer Passport Digital Fun
Khan Academy - Lots of Math Resources, and ability to login and track as a parent or teacher for free at plenty of levels.
Smarter Every Day
Rich Rebuilds - Tesla Mechanics
Adam Savage - Tested
Crash Course - Multiple Liberal Arts and Science Subject Youtube Universe - Some topics are a bit more mature, maybe 4th Grade and Up, all the way to High School chemistry, literature, philosophy, and civics. Fantastic community of learners!