I've never seen anything like this before! The folks over at Sesame Workshop have made an awesome interactive YouTube video. By embedding links to other videos in the first video they have essentially created a "Choose Your Own Adventure" style experience. This one features Cookie Monster and his friend Emma learning about buoyancy and introduces kids to the concepts of the scientific method.
Sesame Workshop has really done something cool and innovative here, and as is their style, it's done with high production value and many teachable moments (Kitty wanted to know what a hypothesis was after watching the clip).