If it's the source I saw I think it counted "children" to age 21 or 25. So if you count a child as someone up to 21 then yes firearms are the leading cause of death. I personally think that's disingenuous. A majority of that number are probably 16-21 year olds in gangs who are killed and not school shootings as a lot of people want to make it sound when they use that statistic.