I'm not sure its the gun thing but do think the grandparents caused it and covered it up. Doubt both caused it but both covered it up in my opinion.
if it is guns, I absolutely think that would be covered up here. Guns are so controversial here and our laws are strict, they would have a lot to lose imo. Also if the family dynamics are already strained I definitely see that tearing the family apart. The dad would obviously have a problem with it, I wouldn't be surprised if that would impact the mums opinion too. In all honesty if I found out my parents left guns around my kids I'd never speak to them again, I know lots of people similar. Even the farm people I grew up with, I know one couple have refused to allow their kids to visit now grandparents because of locked away hunting rifles that they dont even use, so many people are really wary of them. Plus the media outrage would be huge, a child having access to a gun and dying is really not a common thing here. If they didn't want the attention and scrutiny thats another factor.