The Line recently has been been posting process breakdowns showing their animation production line from start to finish.
Their Process follows this Line
1. Rough
2. Tie Down
3. Clean and Colour
4. Shadow
5. Boom!
Obviusly this is streamlined and simplified for the ease of social media and it missed out key stages such as. Character design, storyboard, and layout. But its a helpful insight into how much work goes into even such a simple scene.