The American College of Pediatricians has posted an article about the Impact of Pornography on Children. The article also cites studies that show a negative impact on young adults and adults alike. No one is unaffected. Please take the time to read it, to ponder how to protect our young people, and to commit to being a force for good in what you write.
In the article, Miriam-Webster is cited as defining pornography as "the depiction of erotic behavior (sexual display in pictures or writing) that is intended to cause sexual excitement".1
You can write whatever you want. But before you do, read this article. I know the lean is not toward clean or proper romances, but when we understand how pornography (written or in pictures) affects our society, maybe it's time to take a stand. Stand with me for clean literature, for novels that don't need sex to sell, and against this erosion that is so readily available.
There is a wonderful book listed in the Resources, Good Pictures Bad Pictures by Kristen Jenson and Gayle Poyner, available that you can read with your children that gives them tools to deal with exposure to pornography.
1 http://www.acpeds.org/the-college-speaks/position-statements/the-impact-of-pornography-on-children; "www.merriam-webster.com/dictionary/pornography Accessed 6/4/15"