I'm not sure what is causing the "white" eye, though I suspect it's a reflection from any stage lighting.
Depending on where you sit, a flash may not be of much help. You must be within the flash range (check the manual). You can increase the ISO, but you may get some noise in the image which, imho, is preferable to a blurry photo. Don't forget to change the white balance setting to match the main souce of light in the room.
Here's more information about taking photos at a school play:
http://www.digicamhelp.com/learn/camera-questions-and-answers/taking-photos-at-a-school-play.htm