Pratchett (oddly ds11 didn't like the ones aimed at kids that are similar to other books he likes, but loved Tiffany and then all the Rincewind and City Watch ones).
James Herriot and Gerald Durrell - animals
Antonia Forest's school stories - more grownup than say Blyton. Or the Chalet School (written 1928 to the late 60s)
Little House on the Prairie series
Magical: Diana Wynne Jones (the few for adults are very hard to get hold of so any with modern covers will be good), Barbara Sleigh's Carbonel books, Nevermoor: The Trials of Morrigan Crow
Classics - The Borrowers, Five Children and It, Bedknob and Broomstick, the Hobbit. I've found tellind ds 'some people love this book and others hate it' works quite well.
Agatha Christie's short stories then novels, PG Wodehouse, Sherlock Holmes. I later went on to PD James but they are more adult.
Science fiction - Asimov, Children of Morrow, Chocky and Chocky's Children, collections of short stories.