Some (most?) of my favourite or most enjoyable books seem to be the type that can be enjoyed by both children and adults. Sometimes marketed for children, young adult, nothing in particular, or known as “crossover” or whatever.
Let me list some of my favourites to get the idea 🙂
In no particular order:
The Dark is Rising Sequence, Susan Cooper (re-reading this at the moment. Love it)
Swallows and Amazons (all of ’em), Arthur Ransome
His Dark Materials, Philip Pullman
Harry Potter
Narnia series
The Phantom Tollbooth
Winnie the Pooh! Getting a bit young here, but it’s great 😉
Anything by Joan Aiken, Philippa Pearce, Diana Wynne Jones, Alan Garner (often weirdly disturbing or unsettling), Penelope Lively, Robert Westall
Classics like, um, The Secret Garden or Alice in Wonderland
Ursula Le Guin, Wizard of Earthsea… does that count? Other (generally fantasy) stuff that doesn’t seem to be aimed at anyone in particular, eg Brandon Sanderson
I daresay there’s loads more that escape me at the moment.
Any more? What are your favourites?