"The Kid Should See This" --a collection of videos for curious minds of all ages.
CRASH COURSE KIDS : "Science with a Side Of Awesome" is this YouTube channel's motto. Many will be ready for the channel geared towards older kids (with far more content and on more subjects): CRASH COURSE.
Authors Everywhere! Children's authors and illustrators provide read-alouds, writing tips, art demos, and more to do at home. New videos added regularly.
Science Buddies --tons of shorter STEM activities as well as science projects in all branches of science, beginner to expert.
Science Friday: Educate --STEM experiments, projects, and lesson plans searchable by grade and duration
A+ Click --online math and logic, brainteasers, and more
Jet Propulsion Lab --Launch rockets, build robots, explore your world and beyond! Activities, toolkits, and contests.