In my opinion, I concur with Dr. Marshall that parents need to be supportive of their children. They need to be involved in their children's lives. The closer the relationship between the parent and the child, the more likely the child feels comfortable to confide in the parent if somebody approaches them who probably shouldn't be approaching them.
In my experience, it wouldn't have been likely that this was a random photograph sent to a random cellphone. There was probably some kind of pre-existing relationship there, and if the parent had been aware and cognizant of that relationship and how it was evolving, they might have been able to do something.
But again, I would offer my sincere sympathies to that family. They should have all of the support needed to help their child, particularly given the fact that we know a lot of men who sexually offend have been victims themselves in the past. Therefore, the need for early intervention, treatment, and help for victims of child sexual abuse is absolutely imperative.