Well, my grandson has opened up to us about the incident(s). I hope he's telling the truth, but who knows. Usually when he finally gets over the melt-down stage, he will talk honestly. He assured me that he didn't show that stuff to any younger children, only two older boys, and he would NEVER show such things to girls or young kids. He was kind of horrified that I even asked.
I showed him the website that HopeFilledMama suggested (very good site!) and we looked through it together. That, along with the Technology Use Agreement he had to read for his new school district, answer questions about, and sign--lets him know the importance of his online responsibilities and how easy it is to get into trouble. I wish he had the social skills to be immune to this type of stuff, but he doesn't.
And he said that a young fellow in his class at school snuck a phone onto campus and the end of the school year (June of this year) and was showing this stuff to a group of boys (grandson included) at recess. And I'm sure the other boys thought this kid was the coolest kid on campus that day. I'm sure it happens a lot more than we want to know, but the difference is grandson has such a desperate need to be accepted by his peers that he did the same thing in the neighborhood. I asked him if he felt a strong pull to look at those videos and images, and he said no, they made him feel weird and bad. So, the discussion is open at least and he's willing to talk about it.
But he still isn't getting on tablets, which is probably one of the reasons he's being so cooperative right now. I was born in the morning, but not this morning.