I cannot answer the scientific or medical side of things - but can I congratulate you on being forward thinking enough to consider it?!
I did read someplace a few weeks ago that kids don't go as low on the whole low-carbing thing ... and even if it sounds like you would be using dear son as a guinea pig, it might be worth perhaps doing some reductions in certain carbs and seeing how it goes?
I would maybe concentrate on replacing potatoes with other vegetables (you can mash cauliflower with a little cheese and cream and bake off quickly for a delicious mash) - also consider the portions of rice and pasta that he has, whether some of this could be replaced with protein foods or low carb vegetables? I am not certain he'd notice if the exchange was gradual and you never know what you find him enjoying !!
As to bread - that's a toughie - it's not like you don't already have enough on your "plate" with the gluten intolerance/allergy ... maybe one thing at a time?
As to fruits
personally I don't think children should be restricted with their fruit intake, regardless of diabetes (Again, I'm not an expert and have only een diabetic myself for a month or so) but the kind of fruit you could avoid (such as grapes) contain very high simple sugars and also consider offering very fresh marginally underripe fruit - I get great results from eating a green-ish banana but terribly high bgs from eating a yellow or yellow-brown one.
As I have always maintained, we're all different and you have to experiment!
Good luck and congratulations on having your own mind
J/xxx