Another one who went through this stage. I did a "complete ostrich" and ignored it completey...not a good thing to do. I went to a diabetic camp...and loved it. Mind you, I was the kind of child who was going to enjoy it...I remeber beating the Drs at cricket..and feeling very proud. I was about 9 at the time. Mind you, it was the week of Charles and Di's wedding, so it was a long time ago!
I think that you are doing all the right things to be honest. At 10, he is still a child, and will therefore expect to be nagged...it could be that he relies on you nagging for a bit of attention? I guess 10 is a difficult age anyway, with the change in school looming etc. Maybe, when this happens, and he adjusts to a new school, he wil settle down a bit. I didn't really enjoy the one trip I went on with teh hospital...as I didn't know anyone.
Sorry, I am not being much help. Denial is quite a common thing amoungst diabetics, especially children and teenagers. The best thing you can do is to make sure he stays healthy. the fact that his HbA1C isn't dreadful, is a testament to the fact that you are doing a good job with this, in difficult circumstances. As has been said, going on about complications could just make him give up completely....sometimes, when visiting teh clinic, you do see people who have suffered complications though, People with poor sight being the most obvious for a child. If he is a quiet lad, and enjoys computers and reading etc, then maybe pointing out that he may not be able to do this if he doesn't look after himself might help, but do it in a positive way! It is not inevitable by any means, but doing the best you can will stop this happening. The other thing I would add, is never put a limit on how long he could go with bad control before it happens. (There si no rule any way...some people are unlucky!!) I was told that 6 or 7 years of bad control would lead to complications. Of course I heard...go crazy for 5 years and do something about it then! Not good.
Sorry for the ramble!