I remember watching Tim and Moby in BrainPOP movies in my sixth grade science class. BrainPOP created short animations answering various scientific questions. These animations featured two main characters and tracked their journey to learn new information.
I came across this video explaining how these animations are made. They begin with recording the script, and then the artists create rough sketches in the form of a storyboard to make the process organized. Then, they begin to animate.
They talk about computer generated imagery, or CGI, that is common in movies. BrainPOP, on the other hand, uses flash to create a 2D animation. This is mainly used for short videos and website animations. The illusion of depth is portrayed by drawing background and foreground objects on different transparent layers. When the animation is done, the audio files are synchronized to the movement.
For more information, watch this video: https://www.brainpop.com/artsandmusic/artconcepts/digitalanimation/