When children become immersed in play, it may seem as if they can't tell the difference between reality and fantasy. Have you ever wondered if your child's imaginary playmate was real to your child?
Dramatic play...allows children to differentiate between real and pretend. This is readily apparent when observing children using exaggerated voices to signal that they are playing their roles or in the child that announces, "It's just pretend." It may seem as though a child who has spent several hours engaged in dramatic play has just been "playing around" and has nothing concrete to show for it. On the contrary, the kind of play where a child takes on a role, and learns to interact from within that role, is very valuable to her development.
Source: Leap Frog