I was an avid reader as a child and read sooooo many books. But I'm not sure to what extent they'd appeal to children today (40+ years later) and especially to boys.
My favourite series were the Chalet School books, the Anne of Green Gables books (read some of them as a child and sought out the rest as an adult), the Little House on the Prairie books, the Noel Streatfeild books (not a series exactly but similar themes) and the Little Women books. But I can't see a 9 year old boy being interested in any of these.
Some stand alone books that I loved were:-
'When Hitler Stole Pink Rabbit' by Judith Kerr. I'm sure this needs no introduction.
'I am David' by Anne Holm. A young boy escapes from a concentration camp and travels across Europe in search of his mother.
'The Silver Sword' by Ian Serraillier. This book is about a family living in Poland during WWII. The children have to fend for themselves when their parents are captured by the Nazis.
The latter three books are all set during wartime so the themes/content may be too mature or scary for a 9 year old boy.
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What else?
I loved the Dutch-American author Meindert DeJong. Two of his books were favourites - 'The Wheel on the School' and 'Far out the Long Canal'. 'The Wheel on the School' is about a group of Dutch children who embark on a plan to build a nest to attract storks to their village. It's a simple, charming story. 'Far out the Long Canal' is about a Dutch boy learning to ice skate. Due to illness, he wasn't able to learn to skate at the same time as his peers, so he's really keen to master ice skating and participate like the other kids. I also read 'The House of Sixty Fathers' but didn't enjoy it so much.
I also loved a book about two brothers growing up in Jamaica but I can't remember the title and a quick google hasn't thrown up this particular book.
I think I've ruled out more books than I've recommended, but some of the contributors to the thread might enjoy a trip down memory lane.