This site doesn't have some magical algorithm to detect NSFW images. If someone submits an "unmarked" picture and idiots give it 10s instead of marking it, it'll make it to the top photos. If it horrifies you so much to see naked naughty bits, mark the picture. Posting a NSFW screencap and bitching about it in a bulletin will do absolutely nothing, except get yourself banned for violating the rules. Yeah, it's still against the rules to post NSFW material in bulletins.
As far as your kids seeing those pictures is concerned: don't look at adult-oriented sites when they're around. Sugar-coat it all you want. This is an adult site, and it'll never be 100% work safe.
