A friend of mine had his 13 year old suspended from school recently because he accepted oral sex from 2 of his classmates (who were also suspended). When questioned about it, he was genuinely perplexed for 2 reasons:
He didn't think it was sex
He didn't see a problem because "everybody does it"

My own discussion with doctors in this area suggest this child's thinking is not uncommon and oral sex is seen as a commodity to be traded. Somehow it has become disassociated with intimacy, and is not sex in their eyes. Therefore, they are doing nothing wrong.

Sounds very much like a very high profile politician a few years ago...