How many children are killed each year by gun accidents?

We don't know. An example of one country is the USA, where according to the university of Michigan health system:

http://www.med.umich.edu/yourchild/topics/guns.htm

The 2002 edition of Injury Facts from the National Safety Council reports the following statistics :

  • In 1999, 3,385 children and youth ages 0-19 years were killed with a gun. This includes homicides, suicides, and unintentional injuries.
  • This is equivalent to about 9 deaths per day, a figure commonly used by journalists.
  • The 3,385 firearms-related deaths for age group 0-19 years breaks down to:
    • 214 unintentional
    • 1,078 suicides
    • 1,990 homicides
    • 83 for which the intent could not be determined
    • 20 due to legal intervention
  • Of the total firearms-related deaths:
    • 73 were of children under five years old
    • 416 were children 5-14 years old
    • 2,896 were 15-19 years old