Might I enquire what you are feeding them? Chickens eat to satisfy a daily calorie intake, so they will eat less of a feed that has more calories and more of a feed that has less. Treats such as store bought ones, i.e. mealworms are just too expensive for every day use. Garden treats are ok, but the bird needs to be eating a complete feed ration every day first. Scratch is usually to low in protein to be used as a food, it is cheap… but you are getting what one pays for as well.
Perhaps if feed cost is an issue, you might consider not adding more birds to your flock. It is false economy to feed birds other than a commercially prepared daily ration.
Best to you and your birds,
RJ