If I were you, I wouldn't mention the nsfw content to your parents because that could make them a little more suspicious of the site (though there is a safe-search button you can turn on when you're looking through the tags). I would start by telling them that there aren't any viruses on it (but if you get fan-mails of people asking you to go to their blog and click on a link on it, don't), there's a lot of good content on it, and that it's overall a good website.
Honestly, the only "bad stuff" I've seen on it is the occasional nsfw (like I said before, you can turn on the safe-search filter).