scratch is like candy, they don't need it when they are growing so fast! I didn't even give mine BOSS until they were closer to 8 weeks old, and then only because the adults were getting it when they freeranged together.
I give the youngsters mealworms as "get them friendlier" treats, because I feel that they are pretty darn nutritious for treats. You could use a dab of oatmeal (plain ole breakfast oatmeal) or crumbled up hard-boiled egg yolks, but try to stay away from too many treats when they are growing so fast they need the more concentrated foods
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IF you feed ANY treats at all bring them a couple of tablespoons of gritty sand, or buy chick sized grit, because they'll need it for digestion.