Pardon my lack of familiarity with "the literature" and its standard age groups. Good of you to immediately dismiss the data as "massaged." I couldn't even view your study.
If you've been in the field of science long enough, you learn the smell of bad studies, and this one is patently obvious. But I can look more closely at it if you insist.
As for viewing "my" study, note the "Download Free PDF" button to the upper middle right, all you have to do is supply an email address to do it as a guest. Or ask and I'll put a copy up.
And since your point was couched as a warning to others, another counter is that it's relatively easy to keep your family from joining the bad statistics by gun proofing your kids (which you should do anyway, since you can't control when they might come into contact with one outside your home), and storing your guns responsibly.