I'm glad you saw a airbrushed bush in playboy when you were 12 and turned out fine. My daughter saw some kids real junk, got suspended and potentially could have be punished for having child pornography.
We have talks with our kids about sex, drugs, suicide, murder, death and the like. with cell phones your kids potentially have access to not only everything the internet has to offer, but contact with other kids who don't' have responsible parents that have those conversations. These kids are just a snapchat or text away from communicating and influencing other children.
If it were up to me the kids wouldn't have phones at all. The only thing they should be concerned with is getting a good education, playing sports/activities and having fun. I know everybody has one but great, I dont want my kids to be just like everyone else. Unfortunately my wife and I don't see eye to eye on this and thats an entirely different subject and one I work on daily. Luckily she finally agreed with me after this incident.