What a great question! How could make-believe or pretend play be so important for young children? After all, it is just, well, play!
Research has shown that pretend play is very important for a young child's development in number of ways. First, children develop and hone a number of important social skills in the midst of zooming cars and fort building. In fact, when another child is involved, they are able to practice turn-taking, sharing responsibility (for the direction of play), and creative problem solving. For instance, when the play comes to a stand-still because of a surprising "obstacle", children must think quickly and cooperatively to develop a plan for the next direction of play. Working through these challenges together, lends itself to further social skill development.
In addition, children practice language skills within the context of pretend play. During play, children often experiment with language and voices (e.g., mom calling the children to dinner). Parents and teachers can facilitate this process by introducing new words into the play.
Finally, pretend play inspires the imagination and thinking skills. Pretend play naturally involves the question, "And, what happens next?" If the right creative materials are available, the sky is the limit in answer to that question!
For more on this, please see the following article: