If you copy/paste youtube links into a search box, it creates an ad-free/comment-free link that you can save to access a youtube video for your class. It also eliminates the "suggested videos" that pop up at the end of each video.

This is a great source that provides the similar manipulatives that we use in math- digi blocks, fraction patterns, base tens blocks. Students can manipulate the resources online. In the homepage, you'll see that the manipulatives are organized by grade level and math topic.

For any elementary (or even secondary!) teachers, this is a great site with animated videos for math and science topics. They have tutorials on how to solve different math problems, and explanations on any science topics. You can always pause the video to have discourse when needed.