Ds1 raced through Stormbreaker on holiday a couple of years ago - he would have been the same age then as your ds is, cod. He also read the next two (didn't enjoy them as much) but hasn't read any more. I felt they were a bit old for him then, tbh - I remember reading a bit of one to him and it was about Alex Rider and some girl - and they are being ballboys/girls at Wimbledon and he says something like "Alex hoped she was keeping her eye on the right balls" because she fancies one of the players. And I was a bit Which I know is stupid because I know he hears far worse at school
I got him a boxed set of Michael Morpurgo for Christmas and we are both loving them - I thought of you when I was trying to read (out loud) the last bit of Kensuke's Kingdom. You'll need a big box of tissues for Adolphus Tips - be warned.
The only MM one we've not liked thus far is My Friend Walter.