Every single child (and people under 18 are just that: children) dying because their parents couldn't be arsed to follow even the most basic gun safety laws is one too much. Toddlers shooting themselves with the gun that their reckless father left under the pillow? Even in countries with very liberal attitudes to guns such as Switzerland don't have that problem.
Not to mention, the cutoff at age 18 is obvious because most people have finished education at that age - and the most shootings happen at high school.
So in a country with around 75 million under-18s, that works out to an approximate risk of 1/500,000 per kid per year. And per the article:
> The most likely age group to be both shooters and victims are teenagers ages 14 to 17
Maybe we should make firearms safety and hunters education classes once again part of the school curriculum to prevent these accidents? Just like with driving classes, training and experience in a controlled environment is a great way to reduce the frequency of accidents. Although that assumes the incidents in question are accidents, rather than "accidents".
Not to mention, the cutoff at age 18 is obvious because most people have finished education at that age - and the most shootings happen at high school.