MG Writing 8-12 year olds

I had an MG.
It was British Racing Green and not in the best of condition. 
Someone crashed into it a few weeks after I bought it. 
Ho hum. 
No more MG.

But I digress, don't worry, this is a writing post.
MG  = Middle Grade or 8-12 yr old readers.

My first book- self published was for this age group. Should have researched first, but putting it out in the world has helped me to move along the writing pathway.

My research says-
30-50,000 words max
Child characters 
One major plot arc in a 3 act structure
Modern language- not patronising, not too complicated
Humour
Action
Short chapters with hooks
Fast plot
Little introspection 
Mystery and Possibilities
Hints and clues
Series
No preaching, profanity, graphic violence or sex

Plus, of course, all the usual good writing techniques - dialogue to fit character, grammar, tight writing, active and powerful verbs, show not tell etc...