Young children pre-teens have access to mobile phones nowadys with the approval of their parents many of whom would not monitor what their children use it for .
Keeping in mind the society we live in today children are subject to sexually explicit material on TV ,videos,movies etc especially if the parents are lax in supervising what children can watch.
And children being who they are will find ways to pull the wool over the eyes of their parents being inquisitive about sex.especially if their peers have freedom to view such content.
So YES ,I think sexting in this sense is a very serious problem that many young people are involved in.
The next step is to send photos using your phone of nude or more explicit poses to your boy or girl friend that teenage youths are becoming more prevalent causing all manner of problems for our youth today.And of course this is a serious problem especially when one partner puts pressure on the other to do something out of fear of having it shown to family or friends. (blackmail)
In this case it should be a crime.