Children are learning about emotions all the time; they feel them for themselves, and they see emotions in family and friends. At around 3-4 children will be able to express basic feelings like sad, happy, excited, or angry. They will also experience and understand these feelings in other people.
Under this age they will not have the cognitive skills to understand emotions, so helping children to learn about emotions through play can be helpful.
A re-telling of the story on Youtube: