I told my wife that our 3rd grader had most likely seen porn at school. It turns out I was right. She had several friends in the 5th grade, and about 90% of the fifth graders have smart phones.

My math was simple: if you give 10 twelve-year-olds unfettered internet access, at least one of them will find porn, and that one will show it to their friends. If any of them have an older sibling, the odds just go up.