Stig of the Dump, by Clive King (1963), for Timeslip Tuesday
Eight year old Barney is open about his new friend, Stig--"He's a sort of boy...He just wears rabbit skins and lives in cave." Though his sister and grandmother don't believe in Stig, he is, in fact real, and living in a disused quarry that's rapidly filling up with rubbish. Stig is, indeed, from the Stone Age of Britain, but with considerably ingenuity he turns his hand to the modern rubbish to furnish his home with all mod. cons. (more or less).
In series of episodic adventures, Barney and Stig encounter a group of tough boys, capture an escaped circus leopard, foil would be robbers, disrupt a fox hunt, and cut wood. Each chapter is self contained, making it a good read aloud, and though the stories are not desperately exciting or original, they are told with verve.
What makes the book really fun, though, is Stig's inventiveness. This book should inspire any child who likes to build to have fun with recycled junk. And that modern side of the material world is paired very nicely with the descriptions of Stig's own Stone Age culture.
I wondered, as I read, if we would ever be told definitely that Stig is a time traveller. We don't, exactly, but instead, near the end of the book Barney and his sister become time travellers themselves, visiting Stig and his own people on the edge of the moor as they raise a great cap stone onto two standing stones...This chapter is rather magical, and adds considerably to the sense of wonder in the book as a whole, contrasting, as it does, with Barney's matter of fact acceptance of Stig in the earlier chapters.
Barney is only eight, and sometimes I found his eightness, with its lack of questioning, rather frustrating. But I think that this probably adds to its child reader appeal, and looking over the reviews on Goodreads, this is one that many who read it when they were kids feel great fondness for.
The style might be off-putting to the modern child; it was, after all, published almost fifty years ago. I think the audio book might, however, might make a lovely car trip story, one that might even prompt discussion after the book is done. I can imagine my own boys whiling the miles away (well, at least one or two miles) with imaginative ideas on how discarded objects of modern times might be used by a survivor of the Stone Age.
personal note: I know that kids these days just don't get a chance to get out and explore as much as the pluckier children of bygone days, but I don't think that even back then I'd let my eight year old wander the English countryside alone in all weather, especially if he came home and told me he'd made friends with a strange man in a rubbish dump. This thought kept intruding into the story, in a disruptive kind of way.