I can't immediately recall any sci-fi elements from The Archers myself, so that checks out. Anything to do with the lost precursor civilization tends more towards the archaic future-tech. Like in City Of The Lost God there's a magical weapon that's basically an operational laser gun. Or The Island of the Frozen Seas, which has a palace that looks like a downed spaceship complete with sarcophagi/crypods with people in them.

And you're welcome! I hope you and your son have fun! :)