This is where you have the old problem of not actually having movie ratings on your videos/dvds, USA. I notice that a lot of home video has no age restriction other than the MPAA rating which SOMETIMES appears, but only if rated from the movies. So of course, most anime you get comes without such MPAA ratings, but an 'advisory' age range which mostly gets IGNORED, usually by the sort of people who are now trying to ban it. Such idiots think that because its animated, it's for kids. We all know that that ain't the bloody case.
Perhaps you should have clearer age-restrictions on your dvd packaging, for one, so that discerning parents are aware and make decisions based on it. After that, if they let their kids watch it, it's THEIR problem if they still don't like it. The British Board of Film Classification rates both movie content and dvd/vhs content, and no one under the age described may buy them. I know it's not likely to stop under-ages viewing, ultimately, but it's a preventative step in the right direction. My advice to these knee-jerk activists against anime, is to look carefully at the context, the story, and decide if it's for kids AND if it's really any more 'evil' than Nip/Tuck, The Sopranos, Family Guy, South Park, et al, which the USA produce.