No. A child ringing a doorbell and saying Trick or treat would not be considered a threat to life and limb.
Frm Wiki
“Stand-your-ground law is a law that authorizes a person to protect and defend one’s own life and limb against threat or perceived threat. This law states that an individual has no duty to retreat from any place he/she has a lawful right to be and may use any level of force, including lethal, if he/she reasonably believes he/she faces an imminent and immediate threat of serious bodily harm or death; this is as opposed to duty to retreat laws.
Forty-five U.S. states and the U.S. territory of Guam have adopted the castle doctrine,[1] stating that a person has no duty to retreat when his/her home is attacked.”
You may, however, shoot them for sport as gun season opens 10/15 in most states.