CONTEXT: https://www.cnn.com/2023/01/13/us/newport-news-virginia-shooting-friday/index.html
Assume that the six year old does not understand the concepts of life / death / murder / assault. Can the child be charged with assault or murder? Where are the contours that would preclude charging a child with such a serious crime?
UDPATE: https://abcnews.go.com/US/prosecutor-charge-6-year-accused-shooting-teacher/story?id=97722288
We cannot stipulate that a 6 year old does not understand the concepts of life / death / murder / assault, but that stipulation might be baked into the laws of the jurisdiction. In Washington, a child under age 8 is statutorily incapable of committing a crime. Between 8 and 12, there is a statutory presumption that a child is incapable of committing a crime, but that is rebuttable. The statute says "Children under the age of eight years are incapable of committing crime", and it say nothing about understanding concepts. Florida law used to allow that a 6 year old can commit a crime, then when they arrested a 6 year old, they changed the law. But, the law says
A child younger than 7 years of age may not be taken into custody, arrested, charged, or adjudicated delinquent for a delinquent act or violation of law based on an act occurring before he or she reaches 7 years of age, unless the violation of law is a forcible felony as defined in s. 776.08
so a 6 year old can be arrested (charged, tried, convicted) for murder. Virginia does not appear to have any statute declaring 6 year olds to be categorially incapable of committing a crime. The question of capacity is of course a real consideration – insanity remains a defense against criminal charges.
If charges are to be filed against any party, the mother would likely face a misdemeanor charge for storing a firearm in a manner that could cause injury to a child (while no child was injured, the law seems to read that actual injury to a child does not have to occur so long as the potential for actual injury to a child existed because of the way the gun was stored. A six year old handling a gun and bringing it into an elementary school where he used it to shoot someone would more than meet that requirement.)
It shall be conclusively presumed that no child under the age of ten years can be guilty of any offence.
— Children and Young Persons Act 1933 s.50 as amended by the Children and Young Persons Act 1963
The limit was raised from eight years to ten on 1 February 1964.
A child under the age of 12 years cannot commit an offence.
— Criminal Procedure (Scotland) Act 1995 s.41, as amended by the Age of Criminal Responsibility (Scotland) Act 2019
Scotland's limit came into force in December 2021. Prior to its amendment the limit was eight years.
It shall be conclusively presumed that no child under the age of 10 can be guilty of an offence.
— Criminal Justice (Children) (Northern Ireland) Order 1998, art.3
Northern Ireland's limit came into force on 31 January 1999.
The term you want is the age of criminal responsibility. A child below that has the "defense of infancy." There can also be a period where the child is presumed to be incapable of sufficient understanding, but this can be rebutted. Also, children may be tried in juvenile court instead of adult court, which limits punishments; in Virginia, they must be 14 to be tried as an adult.
It varies from jurisdiction to jurisdiction. Some states do not have a minimum, and in others it ranges from six to ten.
See Criminal Code, s. 13:
No person shall be convicted of an offence in respect of an act or omission on his part while that person was under the age of twelve years.
Even Canada's youth (jeuvenile) offenders regime applies only to those between who are at least 12 but under 18 years old.
