It's a nice demonstration of pinwheel style cookies. However I'd put something else in the cavity than dry granulated sugar, like ganache or jam, as the sugar would go everywhere in the house when it's broken open.
I put mini m&ms in mine :) Kids and adults alike love it
Maybe something else inside, like just a few star confetti sprinkles, fruit filling or mini m&ms like Amy Ruth said :D
Sugar is a mess!
What about adding some red popping candy in the centres for a real 4th July bang!