I think grapes are sweet enough on their own, but my son wanted to try to make his own Sour Patch Kids candy with "less sugar" and this was our compromise. They'd also be great for a tea party or special treat. When I looked up recipes for sugared grapes, most of them used raw egg whites. That wasn't very appealing to me, so I substituted lemon juice to give them a sour flavor.
To make them, we put clean grapes in a bowl. Obviously, we used green but I'm sure any color grapes would work.We added enough lemon juice to wet all the grapes and gave it a stir.
After rolling the grapes in sugar, they were ready to eat. You could also freeze them before eating but we didn't want to wait that long. My son actually didn't like them, but they were a hit with the rest of the family.
Don't forget that grapes can be choking hazards, so be sure you don't give these to young children.