There isn't anything you cannot add to granulated sugar to flavor it, but my all-time favorite, hands-down, is vanilla bean.
My kids and I love baking with this simple-to-make sugar and I have a really good feeling your family will too.
2 c granulated sugar
2 vanilla bean pods
Place sugar in a food processor, if you don't have a food processor, a blender works well too in pulse movements.
Slice vanilla pods in halves, then scrape the inside seeds and add to sugar. Slowly pulse the sugar and beans together until well blended.
Pour your blend into an airtight container for storage.
And don't throw away the vanilla bean pods. Place them on top of the sugar for added flavoring.