Hi Cheryl! I think it totally depends on the selection. We read Plutarch aloud to students as young as 6th grade, in bite-sized chunks. And Shakespeare, of course! Same with poetry - we read Wordsworth and Donne and Hopkins and Burns, etc. to students as young as K, with lots of repetition. Pilgrim's Progress, Dickens, etc. can be read aloud pretty early. Good for you to be reading Inferno with younger children! What a delight.
I could see Les Mis working that way also, although the themes are fairly intense for young children, so that might give me pause. I would avoid explaining anything, but let them tell you what they are understanding (narration), especially if it is a work they will revisit later! I would also add that reading the King James Version of the bible aloud is a great way to expose your children to beautiful language patterns. We use ESV for Bible study, but KJV for all other reading aloud and for composition exercises.
We do use thoughtfully abridged versions (usually older well-written children's versions from excellent authors) for some stories like the Odyssey and the Aeneid. If the tale in its original setting would have been known in the general culture before reading/listening, then it's probably good to familiarize our children with the storyline in that way. In fact, I often have older students read a well-written children's version before they begin a challenging read, especially one from antiquity or Christendom. Otherwise, we pretty much avoid abridged versions of classics, and spend more time with younger students reading fairy tales, fables, and worthy children's lit.