Feeding and caring for a baby turtle is NOT easy. They are delicate creatures. The best thing would be to return it to it's natural home now. If you can't you can try (chopped) earthworms, mealworms, small crickets, some non-citrus fruits, dark leafy greens. If you do give it anything from your yard or garden make sure that it is chemical free (fertilizers, pesticides, weed killers, etc).