Good factual-type books about 1st & 2nd world war for 9yo

[shockedballoon]

DS is asking loads of questions about the world wars - obviously due to coverage of the centenary of armistice day. I'm afraid my own knowledge is not very deep and certainly not enough to satisfy his rampant curiosity, however even after about a week (and some googling on my behalf!)
So does anyone have any tips about good books aimed at 9yo+ that explain the who, how and why of the world wars?

Ignore the rogue 'however' !

Horrible Historues are just right for that age.

Lots of usborne books cover the wars very well.
You can also get ones like When Hitler Stole Pink Rabbit which is an autobiography of Judith Kerr who fled Germany, but it's mostly written as a small girl having an adventure.

War Boy by Michael Foreman.

For some reason DS hasn't taken to Horrible Histories - I think they're fab, but also, not DS.
I'm looking for more fact heavy books rather than story books, almost 'textbook-y' but not quite as dry or detailed as I remember my school books! DS likes his fiction very fantasy-based (wizards, aliens and superheroes etc), but facts very factual if that makes sense?

Bit thanks for suggestion so far though!

The My Story series I remember had a few - written as if ityan autobiography for that age group

I got some exactly like this for my 9 yr old ds from Waterstones

My 9yo dd has just enjoyed this world war 2 diary. Its based on a real girl's diary and is interactive - envelopes to open etc.