The opening scene of act one of The Miracle Worker shows baby Helen having recovered from a serious illness.  Her mother begins to notice something strange about her young daughter.  She waves her hand in front of Helen's face, but the baby has no response.  She cries out, but baby Helen does not seem to notice.  She calls for her husband, who comes quickly.  She frantically explains what happened: "'She can’t see. Look at her eyes.... Or hear. When I screamed she didn’t blink.'"  

This is the moment when Helen's parents realize that her illness has left their bright and vibrant daughter deaf and blind.  The timeline of The Miracle Worker is from this moment until Helen has a moment of realization at the well pump with Miss Sullivan.  This scene and a brief one showing how Miss Sullivan and Helen connect are when the play ends.  

This play shows Helen's life before she can communicate.  It is not about her whole life.  The play instead focuses on Helen's journey to learn how to communicate with the help of her teacher, so it is not important to show what Helen was like as a baby who could see and hear.  The play begins with a dramatic event, which is when Helen's parents realize she is deaf and blind.  This is an effective "hook" for those reading or watching the play.