>>> Plus the dangers of printing a gun aren't that clearcut for a 10 or 12 year old
So explain it. Show the real gun and what happens when one is used and explain what can it do and how dangerous it is. Kids at 12, if they're not mentally damaged, can understand basic safety just fine, and guns are not magic - they are tools, and tools can be dangerous (most homes have lots of dangerous or potentially tools). So kids should be taught not to mess with dangerous tools.
Video games have little to do with it - any kid old enough to meaningfully use a computer can understand difference between fairy tale and reality.