Is the book aimed at the younger reader?

The original book was geared towards a younger audience, but I don't think there was a Young Adults category when it published in 1979. I think adults could read it, but the story is harder to swallow. For instance, as far as I can recall, the book never mentions the children's clothing being washed - in 3 years! They occasionally wear old clothes found in the attic, but not on a daily basis.