My four year old sometimes asks me very random questions .. most recently, a lot of those random questions are geared around my diabetes for some reason.
“Mommy, why do you lick the blood off your fingers? That’s gross.”
“Mommy, why do you give your blood away?” (when I check my blood sugar)
“Mommy, what’s your blood sugar?”
“Mommy, have you checked your blood sugar?”
He is such a smart little boy. And so incredibly intuitive. He sees my routine. I get everyone’s food on the table, then the last thing I do is grab my meter, set it on the table, and wait for him to say Grace, then I check my sugar, so we can eat. So in his little brain, he may not understand what exactly a blood sugar reading is, or diabetes for that matter, but he knows it’s part of me and my routine. And he knows that I have to know that number before I put a bite of food into my mouth.
And I don’t have to explain myself when I have to ask him to be careful sitting by/on me so he doesn’t bump into (aka pull out) my insulin pump.
I’ve said this before, that I hate that diabetes has to even be a part of his life at all. But the fact of the matter is that it’s a part of MY life (a huge part) so it will in turn be a part of his. And I’m glad that he’s so inquisitive about it – I am a firm believer that you’ll never learn new things if you don’t ask questions. 
I don’t think you should feel bad about diabetes — THIS PART of diabetes — being a part of his life. He’s inquisitive and he’s learning, and I’m sure he doesn’t feel deprived of anything because of your routine. Plus, he’s asking the right questions of you – his trusted mother – now, so when he inevitably encounters diabetes in the wild, the typical awkwardness and squeamishness won’t be there.