Parents are excused from the law you suggested they may be violating in South Dakota. It is specifically listed as an affirmative defense to the applicable law.

Have you actually read the laws of South Dakota that apply to your questions? That would be a good place to start. From what I’ve read, it would depend on whether the work was considered to be obscene and the intent of why or how the child was exposed to the work. I don’t find that incidental exposure itself would be criminal unless associated with some nefarious intent but that was not based on anything close to exhaustive research.