No oranges. Citrus is not good for chickens. If you do feed them anything but starter feed you will also need to give them chick-grit -- not poultry grit, but chick-sized grit, or give them access to dirt.
I started feeding them treats from about 1 wk onwards. Greens, stinkbugs, oats, mealworms. All in moderation. Make sure that the feed comprises about 90% of their food intake.