The three stages, also known as Mead's "stages of the self," are language, play and game. These stages are a part of a larger theory on sociological development described in Mead's "Mind, Self and Society."
Mead's first stage of the self, language, occurs when a child uses linguistic means to interact with another. The child consequently takes on a role, linguistically reflecting the attitude of that other.
The second stage, play, occurs when a child pretends to be another person, taking the role of the other completely. Examples of this include playing "doctor" or "nurse."
The third stage, game, is the most complex. It occurs when a child not only takes on a role to play in the game but also interacts with the others playing the game, who also take on roles. In this stage, the child must understand both her own role and the roles of the others playing.