F.B.
It sounds fairly normal to be completely honest, most children go through this curiosity and he's not thinking sex like you are, he curious in difference between boys and girls because they're different, not because he's interested in intercourse, he's too young, which is why he thinks sex is 2 people being naked. Now you should tell him, that we don't kiss our sister like that and we don't touch other people or let other people touch us in those areas, because it's not appropriate, but I think he's probably more curious because you're so freaked about it, he thinks there must be something more. I understand you had a horrible experience and maybe talking to a counselor will help you to deal with that and be better able to teach your children the appropriate behaviors without getting too upset about it. You don't want to have bad feelings about your child or their behavior for something that's fairly normal. Good luck!!