"which even the most ignorant parent can't help but know includes nudity"
I don't know about that. I'm betting that in every city in this country, there are many, many parents who have never set foot in an art museum of any kind. In that case, they'd have no idea what was in there. Since this is the Dallas Art Museum, it's highly unlikely that there are any really scandalous artworks in the place at all. You usually find those in other museums, which usually bear the name "Museum of Modern Art" or some such thing.
If you don't know folks who have never been in any museum more distinguished than some sports hall of fame, you don't get out often enough. I could name a dozen such folks just in my neighborhood.
I'm betting that in every city in this country, there are many, many parents who have never set foot in an art museum of any kind. Don't you think they got dragged to the museums themselves on school field trips when they were kids? Even if they weren't, the existence of art museums is so much a part of the culture, I can't imagine anybody NOT knowing there's nude statues inside. My dad is the strictest Southern Baptist you can imagine and he had no problem signing the permission slips for me back in the Sixties.
If I'm wrong, and these were just standard classical nudes, then these parents need to put their kid in private school, because exposure to real art (not modern crap) museums is a basic part of education, funded by tax dollars even I don't begrudge.