I basically let DS eat what I eat so whenever I have candy I let him have a little piece. Helps keep my eating habits in check too!
He probably has about one sweet treat a day, usually a cookie of some sort. I usually have some sort of candy on the go (licorice scottie dogs from TJs right now) and if I have a piece I bite off a bit for him, usually the head with those
He gets chocolate once or twice a month. If I let him I'm sure he'd eat one of those Lindt 80% a day, remarkably sophisticated palate for a recently minted two year old!
I do let him go a bit crazier on vacation and at holidays. Apart from anything else we were recently in the UK and I found readily available vegan M&M type candies and chocolate buttons. Gotta enjoy that stuff while you can buy it! Today we're having a little b'day party for him and he'll get a whole cupcake for dessert. It's not massively junky, obviously vegan and the frosting is made with agave syrup, but still quite a bit more than he usually gets.
I figure if a 4oz glass of carrot juice is enough to send him on a sugar high he's probably not eating too much sugar elsewhere.