I am a beginning photographer with a Canon Rebel XTI. I'm trying to get indoor portraits of my son, but I can't seem to get non-blurry photos because the shutter speed is too slow as I need to let the light in, however he is moving thus causing the blurriness. Whenever I change the shutter speed, the photos become too dark. If anyone has any tips, techniques or settings on the camera they could suggest that would be most appreciated. Maybe I need a different lens?