I started to read to ds at a bit younger than this. I chose books I enjoyed, but around what I knew were his interests - mostly history especially WWII! Animals were a good bet too, especially saving them.
He'd started wanting a story every night about his soft toys, so I was making them up along the lines of "One day Patch wanted to go to the seaside. So he bought his ticket for the train..." they never did anything much and I was bored silly by it and he unfortunately loved them. 🤣
So I would read the chapters and knew he was enjoying them if he wanted me to continue or even better when I found him reading them to himself.
So I think we started with
Cue for Treason (Geoffrey Trease)
Lone Pine Series (Malcolm Saville)
Narnia Series
Adventure series (Enid Blyton)
Children of Primrose Lane/Tennis Shoes/Curtain Up/House in Cornwall (Noel Streatfield)
Storm Ahead/White Riders/Dolphin Summer/Cargo of Horses/Punchbowl Midnight/The Nightbird/Operation Seagull (Monica Edwards)
The Player's Boy/The Players and the Rebels (Antonia Forest)
Black Riders/House of the Paladin/Emerald Crown (Violet Needham)
Marston Baines series (Malcolm Saville)
Alex Rider Series (Antony Horowich)
The Children who lived in a Barn
The Young Detectives
Fred and I series (John Pudney)
Kestrels Plot adventure
Bannermere Series (Geoffrey Trease)
Swish of the Curtain Series (Pamela Brown)
I am David/The Hostage (Anne Holm)
Various Biggles.
So for some I read all in a series. Sometimes I picked out the ones I thought he'd enjoy. He especially loved the Lone Pine Series, although this did involve me having to go in to school and explain why he'd written "you can tell he's gay by the wicked look in his eye" which was a direct quote from The Gay Dolphin Adventure with 'gay' used in the original way and totally innocent on his part.
He still quotes from some of these (he's 19 now) and it definitely effected his language - he used things like "it's a damn shame" or "chocks away" "gosh" etc. and still does to a certain extent - in fact he infected his friends rather than the other way round.
After these he was about 10/11 and he moved onto the Cherub Series/Henderson boys which I would definitely not recommend for any younger - and if reading on their own definitely older.