I've been meaning to post this science experiment for a while now - we tried growing sugar crystals! It's really easy. My kids thought it was tasty (although I wouldn't eat something that's been sitting on the counter for a few days they thought it was irresistible). You probably have everything you need already. The best thing about this science experiment is that it is only a few hours before you start to see results.
here, and here and I just found a fun science blog here with the same experiment, she has a download to print with instructions!
1. Dissolve as much sugar as you can in boiling water - ours would have worked better if we had added the sugar to the boiling water in the pan, until saturated and clear, instead of pouring boiling water into the sugar. After you have a dissolved mixture in your pan, then pour into a warm glass jar (warm because if cold the glass may break, just run the jar under hot water for a minute).
2. Use cotton or wool string - crystals will not form on some fibers. Also if you plan to eat/try eating the crystals use a weight (like a button) that is non-toxic (instead of a paper clip for example).
3. Put a light, airy cloth over the experiment to keep out dust, making the end result more edible.